Science.gov

Sample records for food webs change

  1. Climate change: A rewired food web

    NASA Astrophysics Data System (ADS)

    Blanchard, Julia L.

    2015-11-01

    Climate change is causing large fish species to move into arctic marine environments. A network analysis finds that these fishes, with their generalist diets, add links to the existing food web that may alter biodiversity and web stability.

  2. Changes in host-parasitoid food web structure with elevation.

    PubMed

    Maunsell, Sarah C; Kitching, Roger L; Burwell, Chris J; Morris, Rebecca J

    2015-03-01

    Gradients in elevation are increasingly used to investigate how species respond to changes in local climatic conditions. Whilst many studies have shown elevational patterns in species richness and turnover, little is known about how food web structure is affected by elevation. Contrasting responses of predator and prey species to elevation may lead to changes in food web structure. We investigated how the quantitative structure of a herbivore-parasitoid food web changes with elevation in an Australian subtropical rain forest. On four occasions, spread over 1 year, we hand-collected leaf miners at twelve sites, along three elevational gradients (between 493 m and 1159 m a.s.l). A total of 5030 insects, including 603 parasitoids, were reared, and summary food webs were created for each site. We also carried out a replicated manipulative experiment by translocating an abundant leaf-mining weevil Platynotocis sp., which largely escaped parasitism at high elevations (≥ 900 m a.s.l.), to lower, warmer elevations, to test if it would experience higher parasitism pressure. We found strong evidence that the environmental change that occurs with increasing elevation affects food web structure. Quantitative measures of generality, vulnerability and interaction evenness decreased significantly with increasing elevation (and decreasing temperature), whilst elevation did not have a significant effect on connectance. Mined plant composition also had a significant effect on generality and vulnerability, but not on interaction evenness. Several relatively abundant species of leaf miner appeared to escape parasitism at higher elevations, but contrary to our prediction, Platynotocis sp. did not experience greater levels of parasitism when translocated to lower elevations. Our study indicates that leaf-mining herbivores and their parasitoids respond differently to environmental conditions imposed by elevation, thus producing structural changes in their food webs. Increasing

  3. Soil food web changes during spontaneous succession at post mining sites: a possible ecosystem engineering effect on food web organization?

    PubMed

    Frouz, Jan; Thébault, Elisa; Pižl, Václav; Adl, Sina; Cajthaml, Tomáš; Baldrián, Petr; Háněl, Ladislav; Starý, Josef; Tajovský, Karel; Materna, Jan; Nováková, Alena; de Ruiter, Peter C

    2013-01-01

    Parameters characterizing the structure of the decomposer food web, biomass of the soil microflora (bacteria and fungi) and soil micro-, meso- and macrofauna were studied at 14 non-reclaimed 1- 41-year-old post-mining sites near the town of Sokolov (Czech Republic). These observations on the decomposer food webs were compared with knowledge of vegetation and soil microstructure development from previous studies. The amount of carbon entering the food web increased with succession age in a similar way as the total amount of C in food web biomass and the number of functional groups in the food web. Connectance did not show any significant changes with succession age, however. In early stages of the succession, the bacterial channel dominated the food web. Later on, in shrub-dominated stands, the fungal channel took over. Even later, in the forest stage, the bacterial channel prevailed again. The best predictor of fungal bacterial ratio is thickness of fermentation layer. We argue that these changes correspond with changes in topsoil microstructure driven by a combination of plant organic matter input and engineering effects of earthworms. In early stages, soil is alkaline, and a discontinuous litter layer on the soil surface promotes bacterial biomass growth, so the bacterial food web channel can dominate. Litter accumulation on the soil surface supports the development of the fungal channel. In older stages, earthworms arrive, mix litter into the mineral soil and form an organo-mineral topsoil, which is beneficial for bacteria and enhances the bacterial food web channel.

  4. Does cadmium pollution change trophic interactions in rockpool food webs?

    SciTech Connect

    Koivisto, S.; Arner, M.; Kautsky, N.

    1997-06-01

    The authors studied the regulation of phytoplankton and zooplankton biomass in rockpool food webs under chronic cadmium pollution. Experimental food webs with two and three trophic levels were composed of phytoplankton, small-bodied zooplankton (Chydorus sphaericus, Cyclops sp., and rotifers), Daphnia magna, and Notonecta sp., a zooplanktivorous predator. Every food web received a control and cadmium treatment allowing a separate study of cadmium and predation effects. After a 3-week stabilization period, cadmium and Notonecta were added and changes in primary productivity, chlorophyll, zooplankton species composition, and biomass were followed during 8 weeks. The results showed that phytoplankton and Daphnia were consumer regulated in both control and cadmium treatments, although resource availability ultimately determined the biomass at each trophic level. Daphnia was the only zooplankton species that reduced phytoplankton and also the only species that was eliminated by Notonecta predation. Notonecta had an indirect positive impact on phytoplankton biomass that increased after the extinction of Daphnia. Cadmium significantly reduced phytoplankton and Daphnia but did not change the trophic interactions between them, i.e., Daphnia and chlorophyll were significantly negatively correlated both in the control and cadmium treatments. Cadmium did not affect the relationship between Daphnia and Notonecta.

  5. Trophic transfer of contaminants in a changing arctic marine food web: Cumberland Sound, Nunavut, Canada.

    PubMed

    McKinney, Melissa A; McMeans, Bailey C; Tomy, Gregg T; Rosenberg, Bruno; Ferguson, Steven H; Morris, Adam; Muir, Derek C G; Fisk, Aaron T

    2012-09-18

    Contaminant dynamics in arctic marine food webs may be impacted by current climate-induced food web changes including increases in transient/subarctic species. We quantified food web organochlorine transfer in the Cumberland Sound (Nunavut, Canada) arctic marine food web in the presence of transient species using species-specific biomagnification factors (BMFs), trophic magnification factors (TMFs), and a multifactor model that included δ(15)N-derived trophic position and species habitat range (transient versus resident), and also considered δ(13)C-derived carbon source, thermoregulatory group, and season. Transient/subarctic species relative to residents had higher prey-to-predator BMFs of biomagnifying contaminants (1.4 to 62 for harp seal, Greenland shark, and narwhal versus 1.1 to 20 for ringed seal, arctic skate, and beluga whale, respectively). For contaminants that biomagnified in a transient-and-resident food web and a resident-only food web scenario, TMFs were higher in the former (2.3 to 10.1) versus the latter (1.7 to 4.0). Transient/subarctic species have higher tissue contaminant levels and greater BMFs likely due to higher energetic requirements associated with long-distance movements or consumption of more contaminated prey in regions outside of Cumberland Sound. These results demonstrate that, in addition to climate change-related long-range transport/deposition/revolatilization changes, increasing numbers of transient/subarctic animals may alter food web contaminant dynamics.

  6. Climate change impacts in multispecies systems: drought alters food web size structure in a field experiment

    PubMed Central

    Woodward, Guy; Brown, Lee E.; Edwards, Francois K.; Hudson, Lawrence N.; Milner, Alexander M.; Reuman, Daniel C.; Ledger, Mark E.

    2012-01-01

    Experimental data from intergenerational field manipulations of entire food webs are scarce, yet such approaches are essential for gauging impacts of environmental change in natural systems. We imposed 2 years of intermittent drought on stream channels in a replicated field trial, to measure food web responses to simulated climate change. Drought triggered widespread losses of species and links, with larger taxa and those that were rare for their size, many of which were predatory, being especially vulnerable. Many network properties, including size–scaling relationships within food chains, changed in response to drought. Other properties, such as connectance, were unaffected. These findings highlight the need for detailed experimental data from different organizational levels, from pairwise links to the entire food web. The loss of not only large species, but also those that were rare for their size, provides a newly refined way to gauge likely impacts that may be applied more generally to other systems and/or impacts. PMID:23007087

  7. Climate change-contaminant interactions in marine food webs: Toward a conceptual framework.

    PubMed

    Alava, Juan José; Cheung, William W L; Ross, Peter S; Sumaila, U Rashid

    2017-02-17

    Climate change is reshaping the way in which contaminants move through the global environment, in large part by changing the chemistry of the oceans and affecting the physiology, health, and feeding ecology of marine biota. Climate change-associated impacts on structure and function of marine food webs, with consequent changes in contaminant transport, fate, and effects, are likely to have significant repercussions to those human populations that rely on fisheries resources for food, recreation, or culture. Published studies on climate change-contaminant interactions with a focus on food web bioaccumulation were systematically reviewed to explore how climate change and ocean acidification may impact contaminant levels in marine food webs. We propose here a conceptual framework to illustrate the impacts of climate change on contaminant accumulation in marine food webs, as well as the downstream consequences for ecosystem goods and services. The potential impacts on social and economic security for coastal communities that depend on fisheries for food are discussed. Climate change-contaminant interactions may alter the bioaccumulation of two priority contaminant classes: the fat-soluble persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), as well as the protein-binding methylmercury (MeHg). These interactions include phenomena deemed to be either climate change dominant (i.e., climate change leads to an increase in contaminant exposure) or contaminant dominant (i.e., contamination leads to an increase in climate change susceptibility). We illustrate the pathways of climate change-contaminant interactions using case studies in the Northeastern Pacific Ocean. The important role of ecological and food web modeling to inform decision-making in managing ecological and human health risks of chemical pollutants contamination under climate change is also highlighted. Finally, we identify the need to develop integrated policies that manage the

  8. Topographically driven predictions for river food webs: responses to land cover and climate change

    NASA Astrophysics Data System (ADS)

    Power, M. E.; Dietrich, W. E.; Finlay, J. C.; Bode, C. A.; Hondzo, M.; Limm, M.; National CenterEarth Surface Dynamics

    2011-12-01

    Fluxes of materials and energy, as well as the performances and interactions of organisms in food webs are strongly influenced by topography and vegetation. We have been using a "predictive mapping" approach to investigate how resource fluxes and food web interactions change down the Eel River drainage network in Northwestern California. In this talk, I will focus on hydrologic and food web controls on the production and fate of dominant primary producers in the river (macroalgae, diatoms and cyanobacteria). Algal mediated processes (e.g. nitrogen-fixation) and processes that limit algal abundance (e.g. grazer control) change abruptly through the season and down drainage networks. Field surveys and mensurative experiments that map the drainage network positions of these changes, and manipulative field experiments that uncover their causes, set the stage for predictive mapping, which is necessary if not sufficient for forecasts of river ecosystem response to changes in climate, land use, or biota.

  9. The Serengeti food web: empirical quantification and analysis of topological changes under increasing human impact.

    PubMed

    de Visser, Sara N; Freymann, Bernd P; Olff, Han

    2011-03-01

    1. To address effects of land use and human overexploitation on wildlife populations, it is essential to better understand how human activities have changed species composition, diversity and functioning. Theoretical studies modelled how network properties change under human-induced, non-random species loss. However, we lack data on realistic species-loss sequences in threatened, real-world food webs to parameterize these models. 2. Here, we present a first size-structured topological food web of one of the most pristine terrestrial ecosystems in the world, the Serengeti ecosystem (Tanzania). The food web consists of 95 grouped nodes and includes both invertebrates and vertebrates ranging from body masses between 10(-7) and 10(4) kg. 3. We study the topological changes in this food web that result from the simulated IUCN-based species-loss sequence representing current species vulnerability to human disturbances in and around this savanna ecosystem. We then compare this realistic extinction scenario with other extinction sequences based on body size and connectance and perform an analysis of robustness of this savanna food web. 4. We demonstrate that real-world species loss in this case starts with the biggest (mega) herbivores and top predators, causing higher predator-prey mass ratios. However, unlike theoretically modelled linear species deletion sequences, this causes poor-connected species to be lost first, while more highly connected species become lost as human impact progresses. This food web shows high robustness to decreasing body size and increasing connectance deletion sequences compared with a high sensitivity to the decreasing connectance deletion scenario. 5. Furthermore, based on the current knowledge of the Serengeti ecosystem, we discuss how the focus on food web topology alone, disregarding nontrophic interactions, may lead to an underestimation of human impacts on wildlife communities, with the number of trophic links affected by a

  10. MONITORING FOOD WEB CHANGES IN TIDE-RESTORED SALT MARSHES: A CARBON STABLE ISOTOPE APPROACH

    EPA Science Inventory

    Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, and Fundulus heteroclitus isotope values (d13C , d15N, d34S) were examined to assess their use as an indicator for changes in food web support functions in tidally-restored sal...

  11. Climate change impacts on body size and food web structure on mountain ecosystems.

    PubMed

    Lurgi, Miguel; López, Bernat C; Montoya, José M

    2012-11-05

    The current distribution of climatic conditions will be rearranged on the globe. To survive, species will have to keep pace with climates as they move. Mountains are among the most affected regions owing to both climate and land-use change. Here, we explore the effects of climate change in the vertebrate food web of the Pyrenees. We investigate elevation range expansions between two time-periods illustrative of warming conditions, to assess: (i) the taxonomic composition of range expanders; (ii) changes in food web properties such as the distribution of links per species and community size-structure; and (iii) what are the specific traits of range expanders that set them apart from the other species in the community-in particular, body mass, diet generalism, vulnerability and trophic position within the food web. We found an upward expansion of species at all elevations, which was not even for all taxonomic groups and trophic positions. At low and intermediate elevations, predator : prey mass ratios were significantly reduced. Expanders were larger, had fewer predators and were, in general, more specialists. Our study shows that elevation range expansions as climate warms have important and predictable impacts on the structure and size distribution of food webs across space.

  12. Climate change impacts on body size and food web structure on mountain ecosystems

    PubMed Central

    Lurgi, Miguel; López, Bernat C.; Montoya, José M.

    2012-01-01

    The current distribution of climatic conditions will be rearranged on the globe. To survive, species will have to keep pace with climates as they move. Mountains are among the most affected regions owing to both climate and land-use change. Here, we explore the effects of climate change in the vertebrate food web of the Pyrenees. We investigate elevation range expansions between two time-periods illustrative of warming conditions, to assess: (i) the taxonomic composition of range expanders; (ii) changes in food web properties such as the distribution of links per species and community size-structure; and (iii) what are the specific traits of range expanders that set them apart from the other species in the community—in particular, body mass, diet generalism, vulnerability and trophic position within the food web. We found an upward expansion of species at all elevations, which was not even for all taxonomic groups and trophic positions. At low and intermediate elevations, predator : prey mass ratios were significantly reduced. Expanders were larger, had fewer predators and were, in general, more specialists. Our study shows that elevation range expansions as climate warms have important and predictable impacts on the structure and size distribution of food webs across space. PMID:23007094

  13. From projected species distribution to food-web structure under climate change.

    PubMed

    Albouy, Camille; Velez, Laure; Coll, Marta; Colloca, Francesco; Le Loc'h, François; Mouillot, David; Gravel, Dominique

    2014-03-01

    Climate change is inducing deep modifications in species geographic ranges worldwide. However, the consequences of such changes on community structure are still poorly understood, particularly the impacts on food-web properties. Here, we propose a new framework, coupling species distribution and trophic models, to predict climate change impacts on food-web structure across the Mediterranean Sea. Sea surface temperature was used to determine the fish climate niches and their future distributions. Body size was used to infer trophic interactions between fish species. Our projections reveal that 54 fish species of 256 endemic and native species included in our analysis would disappear by 2080-2099 from the Mediterranean continental shelf. The number of feeding links between fish species would decrease on 73.4% of the continental shelf. However, the connectance of the overall fish web would increase on average, from 0.26 to 0.29, mainly due to a differential loss rate of feeding links and species richness. This result masks a systematic decrease in predator generality, estimated here as the number of prey species, from 30.0 to 25.4. Therefore, our study highlights large-scale impacts of climate change on marine food-web structure with potential deep consequences on ecosystem functioning. However, these impacts will likely be highly heterogeneous in space, challenging our current understanding of climate change impact on local marine ecosystems.

  14. Nearshore energy subsidies support Lake Michigan fishes and invertebrates following major changes in food web structure

    USGS Publications Warehouse

    Turschak, Benjamin A; Bunnell, David B.; Czesny, Sergiusz J.; Höök, Tomas O.; Janssen, John; Warner, David M.; Bootsma, Harvey A

    2014-01-01

    Aquatic food webs that incorporate multiple energy channels (e.g. nearshore benthic or pelagic) with varying productivity and turnover rates convey stability to biological communities by providing multiple independent energy sources. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and potentially altered the channels through which consumers acquire energy. We used stable C and N isotopes to determine how Lake Michigan food web structure has changed in the past decade, coincident with the expansion of dreissenid mussels, decreased pelagic phytoplankton production and increased nearshore benthic algal production. Fish and invertebrate samples collected from sites around Lake Michigan were analyzed to determine taxa-specific 13C:12C (delta 13C) and 15N:14N (delta 15N) ratios. Sampling took place during two distinct periods, 2002-2003 and 2010-2012, that spanned the period of dreissenid expansion, and included nearshore, pelagic and profundal fish and invertebrate taxa. Magnitude and direction of the 13C shift indicated significantly greater reliance upon nearshore benthic energy sources among nearly all fish taxa as well as profundal invertebrates. Although the mechanisms underlying this 13C shift likely varied among species, possible causes include the transport of benthic algal production to offshore waters and an increased reliance on nearshore prey items. Delta 15N shifts were more variable and of smaller magnitude across taxa although declines in delta 15N among some pelagic fishes may indicate a shift to alternative prey resources. Lake Michigan fishes and invertebrates appear to have responded to dreissenid induced changes in nutrient and energy pathways by switching from pelagic to alternative nearshore energy subsidies. Although large shifts in energy allocation (i.e. pelagic to nearshore benthic) resulting from invasive species appear to have affected total production at upper trophic

  15. Nearshore energy subsidies support Lake Michigan fishes and invertebrates following major changes in food web structure.

    PubMed

    Turschak, Benjamin A; Bunnell, David; Czesny, Sergiusz; Höök, Tomas O; Janssen, John; Warner, David; Bootsma, Harvey A

    2014-05-01

    Aquatic food webs that incorporate multiple energy channels (e.g., nearshore benthic and pelagic) with varying productivity and turnover rates convey stability to biological communities by providing independent energy sources. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and potentially altered the channels through which consumers acquire energy. We used stable C and N isotopes to determine how Lake Michigan food web structure has changed in the past decade, coincident with the expansion of dreissenid mussels, decreased pelagic phytoplankton production, and increased nearshore benthic algal production. Fish and invertebrate samples collected from sites around Lake Michigan were analyzed to determine taxa-specific 13C:12C (delta13C) and 15N:14N (delta15N) ratios. Sampling took place during two distinct periods, 2002-2003 and 2010-2012, that spanned the period of dreissenid expansion, and included nearshore, pelagic and profundal fish and invertebrate taxa. The magnitude and direction of the delta13C shift indicated significantly greater reliance upon nearshore benthic energy sources among nearly all fish taxa as well as profundal invertebrates following dreissenid expansion. Although the mechanisms underlying this delta13C shift likely varied among species, possible causes include the transport of benthic algal production to offshore waters and increased feeding on nearshore prey items by pelagic and profundal species. delta15N shifts were more variable and of smaller magnitude across taxa, although declines in delta15N among some pelagic fishes suggest a shift to alternative prey resources. Lake Michigan fishes and invertebrates appear to have responded to dreissenid-induced changes in nutrient and energy pathways by switching from pelagic to alternative nearshore energy subsidies. Although large shifts in energy allocation (i.e., pelagic to nearshore benthic) resulting from invasive species appear

  16. Warming-induced changes in predation, extinction and invasion in an ectotherm food web.

    PubMed

    Seifert, Linda I; Weithoff, Guntram; Gaedke, Ursula; Vos, Matthijs

    2015-06-01

    Climate change will alter the forces of predation and competition in temperate ectotherm food webs. This may increase local extinction rates, change the fate of invasions and impede species reintroductions into communities. Invasion success could be modulated by traits (e.g., defenses) and adaptations to climate. We studied how different temperatures affect the time until extinction of species, using bitrophic and tritrophic planktonic food webs to evaluate the relative importance of predatory overexploitation and competitive exclusion, at 15 and 25 °C. In addition, we tested how inclusion of a subtropical as opposed to a temperate strain in this model food web affects times until extinction. Further, we studied the invasion success of the temperate rotifer Brachionus calyciflorus into the planktonic food web at 15 and 25 °C on five consecutive introduction dates, during which the relative forces of predation and competition differed. A higher temperature dramatically shortened times until extinction of all herbivore species due to carnivorous overexploitation in tritrophic systems. Surprisingly, warming did not increase rates of competitive exclusion among the tested herbivore species in bitrophic communities. Including a subtropical herbivore strain reduced top-down control by the carnivore at high temperature. Invasion attempts of temperate B. calyciflorus into the food web always succeeded at 15 °C, but consistently failed at 25 °C due to voracious overexploitation by the carnivore. Pre-induction of defenses (spines) in B. calyciflorus before the invasion attempt did not change its invasion success at the high temperature. We conclude that high temperatures may promote local extinctions in temperate ectotherms and reduce their chances of successful recovery.

  17. Dams and downstream aquatic biodiversity: Potential food web consequences of hydrologic and geomorphic change

    SciTech Connect

    Power, M.E.; Dietrich, W.E.; Finlay, J.C.

    1996-11-01

    Responses of rivers and river ecosystems to dams are complex and varied, as they depend on local sediment supplies, geomorphic constraints, climate, dam structure and operation, and key attributes of the biota. Therefore, {open_quotes}one-size-fits-all{close_quotes} prescriptions cannot substitute for local knowledge in developing prescriptions for dam structure and operation to protect local biodiversity. One general principle is self-evident: that biodiversity is best protected in rivers where physical regimes are the most natural. A sufficiently natural regime of flow variation is particularly crucial for river biota and food webs. We review our research and that of others to illustrate the ecological importance of alternating periods of low an high flow, of periodic bed scour, and of floodplain inundation and dewatering. These fluctuations regulate both the life cycles of river biota and species interactions in the food webs that sustain them. Even if the focus of biodiversity conservation efforts is on a target species rather than whole ecosystems, a food web perspective is necessary, because populations of any species depend critically on how their resources, prey, and potential predators also respond to environmental change. In regulated rivers, managers must determine how the frequency, magnitude, and timing of hydrologic events interact to constrain or support species and food webs. Simple ecological modeling, tailored to local systems, may provide a framework and some insight into explaining ecosystem response to dams and should give direction to mitigation efforts. 78 refs.

  18. Farming practices change food web structures in cereal aphid-parasitoid-hyperparasitoid communities.

    PubMed

    Lohaus, Katharina; Vidal, Stefan; Thies, Carsten

    2013-01-01

    Agricultural intensification has been shown to result in a decline in biodiversity across many taxa, but the changes in community structure and species interactions remain little understood. We have analysed and compared the structure of feeding interactions for cereal aphids and their primary and secondary parasitoids in organically and conventionally managed winter wheat fields using quantitative food web metrics (interaction evenness, generality, vulnerability, link density). Despite little variation in the richness of each trophic group, food web structures between the two farming systems differed remarkably. In contrast to common expectations, aphids and primary parasitoids were characterized by (1) a higher evenness of interaction frequencies (interaction evenness) in conventional fields, which cascaded to interactions at the next trophic level, with (2) a higher interaction evenness, (3) a higher ratio of primary parasitoid taxa per secondary parasitoid (generality) and (4) a higher link density. Aphid communities in the organically managed fields almost exclusively consisted of a single ear-colonizing species, Sitobion avenae, while highly fertilized conventional fields were mainly infested by leaf-colonizing aphids that benefit from the nutritional status of winter wheat. In conclusion, agricultural intensification appears to foster the complexity of aphid-parasitoid food webs, thereby not supporting the general expectation on the importance of organic farming practices for species richness and food web complexity.

  19. Fun With Food Webs

    ERIC Educational Resources Information Center

    Smith, Karl D.

    1977-01-01

    Explains an upper elementary game of tag that illustrates energy flow in food webs using candy bars as food sources. A follow-up field trip to a river and five language arts projects are also suggested. (CS)

  20. The Impact of 850,000 Years of Climate Changes on the Structure and Dynamics of Mammal Food Webs

    PubMed Central

    Nenzén, Hedvig K.; Montoya, Daniel; Varela, Sara

    2014-01-01

    Most evidence of climate change impacts on food webs comes from modern studies and little is known about how ancient food webs have responded to climate changes in the past. Here, we integrate fossil evidence from 71 fossil sites, body-size relationships and actualism to reconstruct food webs for six large mammal communities that inhabited the Iberian Peninsula at different times during the Quaternary. We quantify the long-term dynamics of these food webs and study how their structure changed across the Quaternary, a period for which fossil data and climate changes are well known. Extinction, immigration and turnover rates were correlated with climate changes in the last 850 kyr. Yet, we find differences in the dynamics and structural properties of Pleistocene versus Holocene mammal communities that are not associated with glacial-interglacial cycles. Although all Quaternary mammal food webs were highly nested and robust to secondary extinctions, general food web properties changed in the Holocene. These results highlight the ability of communities to re-organize with the arrival of phylogenetically similar species without major structural changes, and the impact of climate change and super-generalist species (humans) on Iberian Holocene mammal communities. PMID:25207754

  1. The impact of 850,000 years of climate changes on the structure and dynamics of mammal food webs.

    PubMed

    Nenzén, Hedvig K; Montoya, Daniel; Varela, Sara

    2014-01-01

    Most evidence of climate change impacts on food webs comes from modern studies and little is known about how ancient food webs have responded to climate changes in the past. Here, we integrate fossil evidence from 71 fossil sites, body-size relationships and actualism to reconstruct food webs for six large mammal communities that inhabited the Iberian Peninsula at different times during the Quaternary. We quantify the long-term dynamics of these food webs and study how their structure changed across the Quaternary, a period for which fossil data and climate changes are well known. Extinction, immigration and turnover rates were correlated with climate changes in the last 850 kyr. Yet, we find differences in the dynamics and structural properties of Pleistocene versus Holocene mammal communities that are not associated with glacial-interglacial cycles. Although all Quaternary mammal food webs were highly nested and robust to secondary extinctions, general food web properties changed in the Holocene. These results highlight the ability of communities to re-organize with the arrival of phylogenetically similar species without major structural changes, and the impact of climate change and super-generalist species (humans) on Iberian Holocene mammal communities.

  2. Climate change alters the structure of arctic marine food webs due to poleward shifts of boreal generalists.

    PubMed

    Kortsch, Susanne; Primicerio, Raul; Fossheim, Maria; Dolgov, Andrey V; Aschan, Michaela

    2015-09-07

    Climate-driven poleward shifts, leading to changes in species composition and relative abundances, have been recently documented in the Arctic. Among the fastest moving species are boreal generalist fish which are expected to affect arctic marine food web structure and ecosystem functioning substantially. Here, we address structural changes at the food web level induced by poleward shifts via topological network analysis of highly resolved boreal and arctic food webs of the Barents Sea. We detected considerable differences in structural properties and link configuration between the boreal and the arctic food webs, the latter being more modular and less connected. We found that a main characteristic of the boreal fish moving poleward into the arctic region of the Barents Sea is high generalism, a property that increases connectance and reduces modularity in the arctic marine food web. Our results reveal that habitats form natural boundaries for food web modules, and that generalists play an important functional role in coupling pelagic and benthic modules. We posit that these habitat couplers have the potential to promote the transfer of energy and matter between habitats, but also the spread of pertubations, thereby changing arctic marine food web structure considerably with implications for ecosystem dynamics and functioning.

  3. Human Impacts and Climate Change Influence Nestedness and Modularity in Food-Web and Mutualistic Networks.

    PubMed

    Takemoto, Kazuhiro; Kajihara, Kosuke

    2016-01-01

    Theoretical studies have indicated that nestedness and modularity-non-random structural patterns of ecological networks-influence the stability of ecosystems against perturbations; as such, climate change and human activity, as well as other sources of environmental perturbations, affect the nestedness and modularity of ecological networks. However, the effects of climate change and human activities on ecological networks are poorly understood. Here, we used a spatial analysis approach to examine the effects of climate change and human activities on the structural patterns of food webs and mutualistic networks, and found that ecological network structure is globally affected by climate change and human impacts, in addition to current climate. In pollination networks, for instance, nestedness increased and modularity decreased in response to increased human impacts. Modularity in seed-dispersal networks decreased with temperature change (i.e., warming), whereas food web nestedness increased and modularity declined in response to global warming. Although our findings are preliminary owing to data-analysis limitations, they enhance our understanding of the effects of environmental change on ecological communities.

  4. Human Impacts and Climate Change Influence Nestedness and Modularity in Food-Web and Mutualistic Networks

    PubMed Central

    Takemoto, Kazuhiro; Kajihara, Kosuke

    2016-01-01

    Theoretical studies have indicated that nestedness and modularity—non-random structural patterns of ecological networks—influence the stability of ecosystems against perturbations; as such, climate change and human activity, as well as other sources of environmental perturbations, affect the nestedness and modularity of ecological networks. However, the effects of climate change and human activities on ecological networks are poorly understood. Here, we used a spatial analysis approach to examine the effects of climate change and human activities on the structural patterns of food webs and mutualistic networks, and found that ecological network structure is globally affected by climate change and human impacts, in addition to current climate. In pollination networks, for instance, nestedness increased and modularity decreased in response to increased human impacts. Modularity in seed-dispersal networks decreased with temperature change (i.e., warming), whereas food web nestedness increased and modularity declined in response to global warming. Although our findings are preliminary owing to data-analysis limitations, they enhance our understanding of the effects of environmental change on ecological communities. PMID:27322185

  5. Properties of food webs

    SciTech Connect

    Pimm, S.L.

    1980-04-01

    On the assumption that systems of interacting species, when perturbed from equilibrium, should return to equilibrium quickly, one can predict four properties of food webs: (1) food chains should be short, (2) species feeding on more than one trophic level (omnivores) should be rare, (3) those species that do feed on more than one trophic level should do so by feeding on species in adjacent trophic levels, and (4) host-parasitoid systems are likely to be exceptions to (1)-(3) when interaction coefficients permit greater trophic complexity. By generating random, model food webs (with many features identical to webs described from a variety of marine, freshwater, and terrestrial systems), it is possible to generate expected values for the number of trophic levels and the degree of omnivory within webs. When compared with these random webs, real world webs are shown to have fewer trophic levels, less omnivory, and very few omnivores feeding on nonadjacent trophic levels. Insect webs are shown to have a greater degree of omnivory than other webs. The confirmation of all these predictions from stability analyses suggests that system stability places necessary, though not sufficient, limitations on the possible shapes of food webs.

  6. Community assembly and food web stability

    SciTech Connect

    Post, W.M.; Pimm, S.L.

    1983-01-01

    The ecological assembly of food webs is considered as a process of predator colonizations and extinctions. The results of computer simulations using predator-prey equations allow us to identify three types of food web stability and examine how they may change through development of food webs. Species turnover stability increases, stability to extensive species extinction remains constant, and local stability to population fluctuations decreases as food web assembly proceeds. 28 references, 7 figures, 3 tables.

  7. Changes in the Lake Michigan food web following dreissenid mussel invasions: A synthesis

    USGS Publications Warehouse

    Madenjian, Charles P.; Bunnell, David B.; Warner, David M.; Pothoven, Steven A.; Fahnenstiel, Gary L.; Nalepa, Thomas F.; Vanderploeg, Henry A.; Tsehaye, Iyob; Claramunt, Randall M.; Clark, Richard D

    2015-01-01

    Using various available time series for Lake Michigan, we examined changes in the Lake Michigan food web following the dreissenid mussel invasions and identified those changes most likely attributable to these invasions, thereby providing a synthesis. Expansion of the quagga mussel (Dreissena rostriformis bugensis) population into deeper waters, which began around 2004, appeared to have a substantial predatory effect on both phytoplankton abundance and primary production, with annual primary production in offshore (> 50 m deep) waters being reduced by about 35% by 2007. Primary production likely decreased in nearshore waters as well, primarily due to predatory effects exerted by the quagga mussel expansion. The drastic decline inDiporeia abundance in Lake Michigan during the 1990s and 2000s has been attributed to dreissenid mussel effects, but the exact mechanism by which the mussels were negatively affecting Diporeia abundance remains unknown. In turn, decreased Diporeiaabundance was associated with reduced condition, growth, and/or energy density in alewife (Alosa pseudoharengus), lake whitefish (Coregonus clupeaformis), deepwater sculpin (Myoxocephalus thompsonii), and bloater (Coregonus hoyi). However, lake-wide biomass of salmonines, top predators in the food web, remained high during the 2000s, and consumption of alewives by salmonines actually increased between the 1980–1995 and 1996–2011 time periods. Moreover, abundance of the lake whitefish population, which supports Lake Michigan's most valuable commercial fishery, remained at historically high levels during the 2000s. Apparently, counterbalancing mechanisms operating within the complex Lake Michigan food web have enabled salmonines and lake whitefish to retain relatively high abundances despite reduced primary production.

  8. Changes in fish diets and food web mercury bioaccumulation induced by an invasive planktivorous fish

    USGS Publications Warehouse

    Eagles-Smith, Collin A.; Suchanek, Thomas H.; Colwell, Arthur E.; Anderson, Norman L.; Moyle, Peter B.

    2008-01-01

    The invasion, boom, collapse, and reestablishment of a population of the planktivorous threadfin shad in Clear Lake, California, USA, were documented over a 20-year period, as were the effects of changing shad populations on diet and mercury (Hg) bioaccumulation in nearshore fishes. Threadfin shad competitively displaced other planktivorous fish in the lake, such as inland silversides, young-of-year (YOY) largemouth bass, and YOY bluegill, by reducing zooplankton abundance. As a result, all three species shifted from a diet that was dominated by zooplankton to one that was almost entirely zoobenthos. Stable carbon isotopes corroborated this pattern with each species becoming enriched in δ13C, which is elevated in benthic vs. pelagic organisms. Concomitant with these changes, Hg concentrations increased by ∼50% in all three species. In contrast, obligate benthivores such as prickly sculpin showed no relationship between diet or δ13C and the presence of threadfin shad, suggesting that effects of the shad were not strongly linked to the benthic fish community. There were also no changes in Hg concentrations of prickly sculpin. The temporary extirpation of threadfin shad from the lake resulted in zooplankton densities, foraging patterns, isotope ratios, and Hg concentrations in pelagic fishes returning to pre-shad values. These results indicate that even transient perturbations of the structure of freshwater food webs can result in significant alterations in the bioaccumulation of Hg and that food webs in lakes can be highly resilient.

  9. Insect-damaged fossil leaves record food web response to ancient climate change and extinction.

    PubMed

    Wilf, P

    2008-01-01

    Plants and herbivorous insects have dominated terrestrial ecosystems for over 300 million years. Uniquely in the fossil record, foliage with well-preserved insect damage offers abundant and diverse information both about producers and about ecological and sometimes taxonomic groups of consumers. These data are ideally suited to investigate food web response to environmental perturbations, and they represent an invaluable deep-time complement to neoecological studies of global change. Correlations between feeding diversity and temperature, between herbivory and leaf traits that are modulated by climate, and between insect diversity and plant diversity can all be investigated in deep time. To illustrate, I emphasize recent work on the time interval from the latest Cretaceous through the middle Eocene (67-47 million years ago (Ma)), including two significant events that affected life: the end-Cretaceous mass extinction (65.5 Ma) and its ensuing recovery; and globally warming temperatures across the Paleocene-Eocene boundary (55.8 Ma). Climatic effects predicted from neoecology generally hold true in these deep-time settings. Rising temperature is associated with increased herbivory in multiple studies, a result with major predictive importance for current global warming. Diverse floras are usually associated with diverse insect damage; however, recovery from the end-Cretaceous extinction reveals uncorrelated plant and insect diversity as food webs rebuilt chaotically from a drastically simplified state. Calibration studies from living forests are needed to improve interpretation of the fossil data.

  10. Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web.

    PubMed

    Niiranen, Susa; Yletyinen, Johanna; Tomczak, Maciej T; Blenckner, Thorsten; Hjerne, Olle; Mackenzie, Brian R; Müller-Karulis, Bärbel; Neumann, Thomas; Meier, H E Markus

    2013-11-01

    Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multimodel approach to project how the interaction of climate, nutrient loads, and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, whereas low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, nonlinearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context.

  11. Changes in food web structure affect rate of PCB decline in herring gull (Larus argentatus) eggs

    SciTech Connect

    Hebert, C.E.; Hobson, K.A.; Shutt, J.L.

    2000-05-01

    Biological monitors provide important information regarding temporal trends in levels of persistent organic pollutants. Correct interpretation of these trends is critical if one is to accurately assess his progress in eliminating these contaminants from the environment. In the Laurentian Great Lakes, polychlorinated biphenyl concentrations in herring gull eggs declined during the 1970s and early 1980s. By the mid-1980s, further declines were not as obvious. An exception to this trend was observed in eggs from Lake Erie. On that lake, egg PCB concentrations continued to decline rapidly during the 1980s/1990s. Evidence from stable isotope analysis indicated that temporal changes in the composition of the herring gull diet occurred on Lake Erie. In the eastern basin, declines in fish availability may have forced the gulls to incorporate a greater proportion of terrestrial food into their diets. Decreases in the proportion of fish in the gull diet would have resulted in reduced PCB exposure. This may be partially responsible for the continuing rapid rate of decline in egg PCB concentrations. This decline should be interpreted with caution. These trends may not be indicative of lake-wide declines in PCB bioavailability but only reflect changes in dietary exposure brought about by alterations in food web structure.

  12. Lake Michigan offshore ecosystem structure and food web changes from 1987 to 2008

    USGS Publications Warehouse

    Rogers, Mark W.; Bunnell, David B.; Madenjian, Charles P.; Warner, David M.

    2014-01-01

    Ecosystems undergo dynamic changes owing to species invasions, fisheries management decisions, landscape modifications, and nutrient inputs. At Lake Michigan, new invaders (e.g., dreissenid mussels (Dreissena spp.), spiny water flea (Bythotrephes longimanus), round goby (Neogobius melanostomus)) have proliferated and altered energy transfer pathways, while nutrient concentrations and stocking rates to support fisheries have changed. We developed an ecosystem model to describe food web structure in 1987 and ran simulations through 2008 to evaluate changes in biomass of functional groups, predator consumption, and effects of recently invading species. Keystone functional groups from 1987 were identified as Mysis, burbot (Lota lota), phytoplankton, alewife (Alosa pseudoharengus), nonpredatory cladocerans, and Chinook salmon (Oncorhynchus tshawytscha). Simulations predicted biomass reductions across all trophic levels and predicted biomasses fit observed trends for most functional groups. The effects of invasive species (e.g., dreissenid grazing) increased across simulation years, but were difficult to disentangle from other changes (e.g., declining offshore nutrient concentrations). In total, our model effectively represented recent changes to the Lake Michigan ecosystem and provides an ecosystem-based tool for exploring future resource management scenarios.

  13. Local food web management increases resilience and buffers against global change effects on freshwaters

    PubMed Central

    Urrutia-Cordero, Pablo; Ekvall, Mattias K.; Hansson, Lars-Anders

    2016-01-01

    A major challenge for ecological research is to identify ways to improve resilience to climate-induced changes in order to secure the ecosystem functions of natural systems, as well as ecosystem services for human welfare. With respect to aquatic ecosystems, interactions between climate warming and the elevated runoff of humic substances (brownification) may strongly affect ecosystem functions and services. However, we hitherto lack the adaptive management tools needed to counteract such global-scale effects on freshwater ecosystems. Here we show, both experimentally and using monitoring data, that predicted climatic warming and brownification will reduce freshwater quality by exacerbating cyanobacterial growth and toxin levels. Furthermore, in a model based on long-term data from a natural system, we demonstrate that food web management has the potential to increase the resilience of freshwater systems against the growth of harmful cyanobacteria, and thereby that local efforts offer an opportunity to secure our water resources against some of the negative impacts of climate warming and brownification. This allows for novel policy action at a local scale to counteract effects of global-scale environmental change, thereby providing a buffer period and a safer operating space until climate mitigation strategies are effectively established. PMID:27386957

  14. Effects of food web changes on Mysis diluviana diet in Lake Ontario

    USGS Publications Warehouse

    O'Malley, Brian P.; Rudstam, Lars G.; Watkins, James M.; Holda, Toby J.; Weidel, Brian C.

    2017-01-01

    Mysids are important benthic-pelagic omnivores in many deep-lake food webs, yet quantitative data on their diet are limited. We explored the trophic role of Mysis diluviana in offshore Lake Ontario using samples collected in May, July, and September 2013 with a focus on seasonal and ontogenetic patterns in herbivory and zooplanktivory using two approaches. We hypothesized that Mysis diet in 2013 differs from the last investigation in 1995 in response to changes in pelagic prey over 1995 to 2013. Gut fluorescence indicated high grazing by adult and juvenile Mysis in May 2013. In July, smaller mysids were more herbivorous than larger individuals, a pattern that was less pronounced in September. Microscopic gut analysis showed copepods, including Limnocalanus, were common in diets of both size groups in May. In July, mainly cladocerans were consumed, including Cercopagis pengoi which represents a change from a past investigation that preceded Cercopagis invasion in the lake. Our results are consistent with earlier observations of a larger proportion of algae in mysid diets in spring, transitioning to relatively more zooplanktivory and use of cladocerans in the summer and fall. Higher chlorophyll content in small mysids in July than in September may be associated with the presence of a deep chlorophyll layer in July that had largely dissipated by September. Overall, Mysis in Lake Ontario continues to be a generalist omnivore, incorporating new prey items and exhibiting higher herbivory in spring.

  15. Local food web management increases resilience and buffers against global change effects on freshwaters.

    PubMed

    Urrutia-Cordero, Pablo; Ekvall, Mattias K; Hansson, Lars-Anders

    2016-07-08

    A major challenge for ecological research is to identify ways to improve resilience to climate-induced changes in order to secure the ecosystem functions of natural systems, as well as ecosystem services for human welfare. With respect to aquatic ecosystems, interactions between climate warming and the elevated runoff of humic substances (brownification) may strongly affect ecosystem functions and services. However, we hitherto lack the adaptive management tools needed to counteract such global-scale effects on freshwater ecosystems. Here we show, both experimentally and using monitoring data, that predicted climatic warming and brownification will reduce freshwater quality by exacerbating cyanobacterial growth and toxin levels. Furthermore, in a model based on long-term data from a natural system, we demonstrate that food web management has the potential to increase the resilience of freshwater systems against the growth of harmful cyanobacteria, and thereby that local efforts offer an opportunity to secure our water resources against some of the negative impacts of climate warming and brownification. This allows for novel policy action at a local scale to counteract effects of global-scale environmental change, thereby providing a buffer period and a safer operating space until climate mitigation strategies are effectively established.

  16. Local food web management increases resilience and buffers against global change effects on freshwaters

    NASA Astrophysics Data System (ADS)

    Urrutia-Cordero, Pablo; Ekvall, Mattias K.; Hansson, Lars-Anders

    2016-07-01

    A major challenge for ecological research is to identify ways to improve resilience to climate-induced changes in order to secure the ecosystem functions of natural systems, as well as ecosystem services for human welfare. With respect to aquatic ecosystems, interactions between climate warming and the elevated runoff of humic substances (brownification) may strongly affect ecosystem functions and services. However, we hitherto lack the adaptive management tools needed to counteract such global-scale effects on freshwater ecosystems. Here we show, both experimentally and using monitoring data, that predicted climatic warming and brownification will reduce freshwater quality by exacerbating cyanobacterial growth and toxin levels. Furthermore, in a model based on long-term data from a natural system, we demonstrate that food web management has the potential to increase the resilience of freshwater systems against the growth of harmful cyanobacteria, and thereby that local efforts offer an opportunity to secure our water resources against some of the negative impacts of climate warming and brownification. This allows for novel policy action at a local scale to counteract effects of global-scale environmental change, thereby providing a buffer period and a safer operating space until climate mitigation strategies are effectively established.

  17. Estimating effects of tidal power projects and climate change on threatened and endangered marine species and their food web.

    PubMed

    Busch, D Shallin; Greene, Correigh M; Good, Thomas P

    2013-12-01

    Marine hydrokinetic power projects will operate as marine environments change in response to increased atmospheric carbon dioxide concentrations. We considered how tidal power development and stressors resulting from climate change may affect Puget Sound species listed under the U.S. Endangered Species Act (ESA) and their food web. We used risk tables to assess the singular and combined effects of tidal power development and climate change. Tidal power development and climate change posed risks to ESA-listed species, and risk increased with incorporation of the effects of these stressors on predators and prey of ESA-listed species. In contrast, results of a model of strikes on ESA-listed species from turbine blades suggested that few ESA-listed species are likely to be killed by a commercial-scale tidal turbine array. We applied scenarios to a food web model of Puget Sound to explore the effects of tidal power and climate change on ESA-listed species using more quantitative analytical techniques. To simulate development of tidal power, we applied results of the blade strike model. To simulate environmental changes over the next 50 years, we applied scenarios of change in primary production, plankton community structure, dissolved oxygen, ocean acidification, and freshwater flooding events. No effects of tidal power development on ESA-listed species were detected from the food web model output, but the effects of climate change on them and other members of the food web were large. Our analyses exemplify how natural resource managers might assess environmental effects of marine technologies in ways that explicitly incorporate climate change and consider multiple ESA-listed species in the context of their ecological community. Estimación de los Efectos de Proyectos de Energía de las Mareas y el Cambio Climático sobre Especies Marinas Amenazadas y en Peligro y su Red Alimentaria.

  18. The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe

    PubMed Central

    Yeakel, Justin D.; Guimarães, Paulo R.; Bocherens, Hervé; Koch, Paul L.

    2013-01-01

    Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before—and possibly after—the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities. PMID:23658198

  19. The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe.

    PubMed

    Yeakel, Justin D; Guimarães, Paulo R; Bocherens, Hervé; Koch, Paul L

    2013-07-07

    Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before--and possibly after--the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities.

  20. Genotype matching in a parasitoid-host genotypic food web: an approach for measuring effects of environmental change.

    PubMed

    Lavandero, Blas; Tylianakis, Jason M

    2013-01-01

    Food webs typically quantify interactions between species, whereas evolution operates through the success of alleles within populations of a single species. To bridge this gap, we quantify genotypic interaction networks among individuals of a single specialized parasitoid species and its obligate to cyclically parthenogenetic aphid host along a climatic gradient. As a case study for the kinds of questions genotype food webs could be used to answer, we show that genetically similar parasitoids became more likely to attack genetically similar hosts in warmer sites (i.e. there was network-wide congruence between the within-species shared allelic distance of the parasitoid and that of its host). Narrowing of host-genotype-niche breadth by parasitoids could reduce resilience of the network to changes in host genetic structure or invasion by novel host genotypes and inhibit biological control. Thus, our approach can be easily used to detect changes to sub-species-level food webs, which may have important ecological and evolutionary implications, such as promoting host-race specialization or the accelerated loss of functional diversity following extinctions of closely related genotypes.

  1. The Great Lakes Food Web.

    ERIC Educational Resources Information Center

    Baker, Marjane L.

    1997-01-01

    Presents a play for students in grades four to nine that incorporates the scientific names, physical characteristics, feeding habits, interactions, and interdependence of the plants and animals that make up the Great Lakes food web to facilitate the learning of this complex system. Includes a Great Lakes food web chart. (AIM)

  2. Sustainable Materials Management (SMM) Web Academy Webinar: Changing How We Think About Our Resources for a Better Tomorrow: How to Donate Surplus Food from K-12 Schools

    EPA Pesticide Factsheets

    This is a webinar page for the Sustainable Management of Materials (SMM) Web Academy webinar titled Changing How We Think About Our Resources for a Better Tomorrow: How to Donate Surplus Food from K-12 Schools

  3. Food Web Topology in High Mountain Lakes

    PubMed Central

    Sánchez-Hernández, Javier; Cobo, Fernando; Amundsen, Per-Arne

    2015-01-01

    Although diversity and limnology of alpine lake systems are well studied, their food web structure and properties have rarely been addressed. Here, the topological food webs of three high mountain lakes in Central Spain were examined. We first addressed the pelagic networks of the lakes, and then we explored how food web topology changed when benthic biota was included to establish complete trophic networks. We conducted a literature search to compare our alpine lacustrine food webs and their structural metrics with those of 18 published lentic webs using a meta-analytic approach. The comparison revealed that the food webs in alpine lakes are relatively simple, in terms of structural network properties (linkage density and connectance), in comparison with lowland lakes, but no great differences were found among pelagic networks. The studied high mountain food webs were dominated by a high proportion of omnivores and species at intermediate trophic levels. Omnivores can exploit resources at multiple trophic levels, and this characteristic might reduce competition among interacting species. Accordingly, the trophic overlap, measured as trophic similarity, was very low in all three systems. Thus, these alpine networks are characterized by many omnivorous consumers with numerous prey species and few consumers with a single or few prey and with low competitive interactions among species. The present study emphasizes the ecological significance of omnivores in high mountain lakes as promoters of network stability and as central players in energy flow pathways via food partitioning and enabling energy mobility among trophic levels. PMID:26571235

  4. Food Web Topology in High Mountain Lakes.

    PubMed

    Sánchez-Hernández, Javier; Cobo, Fernando; Amundsen, Per-Arne

    2015-01-01

    Although diversity and limnology of alpine lake systems are well studied, their food web structure and properties have rarely been addressed. Here, the topological food webs of three high mountain lakes in Central Spain were examined. We first addressed the pelagic networks of the lakes, and then we explored how food web topology changed when benthic biota was included to establish complete trophic networks. We conducted a literature search to compare our alpine lacustrine food webs and their structural metrics with those of 18 published lentic webs using a meta-analytic approach. The comparison revealed that the food webs in alpine lakes are relatively simple, in terms of structural network properties (linkage density and connectance), in comparison with lowland lakes, but no great differences were found among pelagic networks. The studied high mountain food webs were dominated by a high proportion of omnivores and species at intermediate trophic levels. Omnivores can exploit resources at multiple trophic levels, and this characteristic might reduce competition among interacting species. Accordingly, the trophic overlap, measured as trophic similarity, was very low in all three systems. Thus, these alpine networks are characterized by many omnivorous consumers with numerous prey species and few consumers with a single or few prey and with low competitive interactions among species. The present study emphasizes the ecological significance of omnivores in high mountain lakes as promoters of network stability and as central players in energy flow pathways via food partitioning and enabling energy mobility among trophic levels.

  5. Phytoplankton fuels Delta food web

    USGS Publications Warehouse

    Jassby, Alan D.; Cloern, James E.; Muller-Solger, A. B.

    2003-01-01

    Populations of certain fishes and invertebrates in the Sacramento-San Joaquin Delta have declined in abundance in recent decades and there is evidence that food supply is partly responsible. While many sources of organic matter in the Delta could be supporting fish populations indirectly through the food web (including aquatic vegetation and decaying organic matter from agricultural drainage), a careful accounting shows that phytoplankton is the dominant food source. Phytoplankton, communities of microscopic free-floating algae, are the most important food source on a Delta-wide scale when both food quantity and quality are taken into account. These microscopic algae have declined since the late 1960s. Fertilizer and pesticide runoff do not appear to be playing a direct role in long-term phytoplankton changes; rather, species invasions, increasing water transparency and fluctuations in water transport are responsible. Although the potential toxicity of herbicides and pesticides to plank- ton in the Delta is well documented, the ecological significance remains speculative. Nutrient inputs from agricultural runoff at current levels, in combination with increasing transparency, could result in harmful al- gal blooms. 

  6. Widespread crown condition decline, food web disruption, and amplified tree mortality with increased climate change-type drought.

    PubMed

    Carnicer, Jofre; Coll, Marta; Ninyerola, Miquel; Pons, Xavier; Sánchez, Gerardo; Peñuelas, Josep

    2011-01-25

    Climate change is progressively increasing severe drought events in the Northern Hemisphere, causing regional tree die-off events and contributing to the global reduction of the carbon sink efficiency of forests. There is a critical lack of integrated community-wide assessments of drought-induced responses in forests at the macroecological scale, including defoliation, mortality, and food web responses. Here we report a generalized increase in crown defoliation in southern European forests occurring during 1987-2007. Forest tree species have consistently and significantly altered their crown leaf structures, with increased percentages of defoliation in the drier parts of their distributions in response to increased water deficit. We assessed the demographic responses of trees associated with increased defoliation in southern European forests, specifically in the Iberian Peninsula region. We found that defoliation trends are paralleled by significant increases in tree mortality rates in drier areas that are related to tree density and temperature effects. Furthermore, we show that severe drought impacts are associated with sudden changes in insect and fungal defoliation dynamics, creating long-term disruptive effects of drought on food webs. Our results reveal a complex geographical mosaic of species-specific responses to climate change-driven drought pressures on the Iberian Peninsula, with an overwhelmingly predominant trend toward increased drought damage.

  7. Changes in Sport Fish Mercury Concentrations from Food Web Shifts Suggest Partial Decoupling from Atmospheric Deposition in Two Colorado Reservoirs.

    PubMed

    Wolff, Brian A; Johnson, Brett M; Lepak, Jesse M

    2017-02-01

    Partial decoupling of mercury (Hg) loading and observed Hg concentrations ([Hg]) in biotic and abiotic samples has been documented in aquatic systems. We studied two Colorado reservoirs to test whether shifts in prey for sport fish would lead to changes in [Hg] independent of external atmospheric Hg deposition. We compared sport fish total mercury concentrations ([T-Hg]) and macroinvertebrate (chironomids and crayfish) methylmercury concentrations ([MeHg]) before and after food web shifts occurred in both reservoirs. We also monitored wet atmospheric Hg deposition and sediment [T-Hg] and [MeHg] at each reservoir. We found rapid shifts in Hg bioaccumulation in each reservoir's sport fish, and these changes could not be attributed to atmospheric Hg deposition. Our study shows that trends in atmospheric deposition, environmental samples (e.g., sediments), and samples of species at the low trophic levels (e.g., chironomids and crayfish) may not accurately reflect conditions that result in fish consumption advisories for high trophic level sport fish. We suggest that in the short-term, monitoring fish [Hg] is necessary to adequately protect human health because natural and anthropogenic perturbations to aquatic food-webs that affect [Hg] in sport fish will continue regardless of trends in atmospheric deposition.

  8. Cestodes change the isotopic signature of brine shrimp, Artemia, hosts: implications for aquatic food webs.

    PubMed

    Sánchez, Marta I; Varo, Nico; Matesanz, Cristina; Ramo, Cristina; Amat, Juan A; Green, Andy J

    2013-01-01

    To reach the final host (greater flamingos), the cestode Flamingolepis liguloides alters the behaviour of its intermediate host, the brine shrimp, Artemia parthenogenetica, causing it to spend more time close to the water surface. During summer 2010, we showed that the prevalence of this cestode was consistently higher at the top of the water column in the Odiel salt pans in south-western Spain. We used stable nitrogen (N) and carbon (C) isotopic analysis to test the hypothesis that cestodes also alter resource use by Artemia. In early summer, we compared stable isotopes in infected hosts at the surface with those from uninfected hosts at the bottom of the water column. In late summer, we compared infected and uninfected Artemia from the bottom. δ(15)N was consistently enriched in infected individuals compared with uninfected hosts, especially in Artemia with multiple infections of F. liguloides (family Hymenolepididae) and those with mixed infections of F. liguloides and cestodes of the family Dilepididae. Infected individuals from the surface were enriched in δ(13)C compared with uninfected ones from the bottom, but the opposite was found when comparing uninfected and infected Artemia from the same depth. This may be caused by the increase in lipid concentration in infected Artemia. Isolated cysticercoids of F. liguloides were significantly enriched in δ(13)C compared with cysticercoids in infected hosts, but surprisingly were not enriched in N. Our findings illustrate the way cestodes can alter food webs and highlight the importance of considering the parasitic status of prey in studies of trophic ecology in saline wetlands.

  9. Parasites in the Wadden Sea food web

    NASA Astrophysics Data System (ADS)

    Thieltges, David W.; Engelsma, Marc Y.; Wendling, Carolin C.; Wegner, K. Mathias

    2013-09-01

    While the free-living fauna of the Wadden Sea has received much interest, little is known on the distribution and effects of parasites in the Wadden Sea food web. However, recent studies on this special type of trophic interaction indicate a high diversity of parasites in the Wadden Sea and suggest a multitude of effects on the hosts. This also includes effects on specific predator-prey relationships and the general structure of the food web. Focussing on molluscs, a major group in the Wadden Sea in terms of biomass and abundance and an important link between primary producers and predators, we review existing studies and exemplify the ecological role of parasites in the Wadden Sea food web. First, we give a brief inventory of parasites occurring in the Wadden Sea, ranging from microparasites (e.g. protozoa, bacteria) to macroparasites (e.g. helminths, parasitic copepods) and discuss the effects of spatial scale on heterogeneities in infection levels. We then demonstrate how parasites can affect host population dynamics by acting as a strong mortality factor, causing mollusc mass mortalities. In addition, we will exemplify how parasites can mediate the interaction strength of predator-prey relationships and affect the topological structure of the Wadden Sea food web as a whole. Finally, we highlight some ongoing changes regarding parasitism in the Wadden Sea in the course of global change (e.g. species introduction, climate change) and identify important future research questions to entangle the role of parasites in the Wadden Sea food web.

  10. Bacterioplankton communities of Crater Lake, OR: Dynamic changes with euphotic zone food web structure and stable deep water populations

    USGS Publications Warehouse

    Urbach, E.; Vergin, K.L.; Larson, G.L.; Giovannoni, S.J.

    2007-01-01

    The distribution of bacterial and archaeal species in Crater Lake plankton varies dramatically over depth and with time, as assessed by hybridization of group-specific oligonucleotides to RNA extracted from lakewater. Nonmetric, multidimensional scaling (MDS) analysis of relative bacterial phylotype densities revealed complex relationships among assemblages sampled from depth profiles in July, August and September of 1997 through 1999. CL500-11 green nonsulfur bacteria (Phylum Chloroflexi) and marine Group I crenarchaeota are consistently dominant groups in the oxygenated deep waters at 300 and 500 m. Other phylotypes found in the deep waters are similar to surface and mid-depth populations and vary with time. Euphotic zone assemblages are dominated either by ??-proteobacteria or CL120-10 verrucomicrobia, and ACK4 actinomycetes. MDS analyses of euphotic zone populations in relation to environmental variables and phytoplankton and zooplankton population structures reveal apparent links between Daphnia pulicaria zooplankton population densities and microbial community structure. These patterns may reflect food web interactions that link kokanee salmon population densities to community structure of the bacterioplankton, via fish predation on Daphnia with cascading consequences to Daphnia bacterivory and predation on bacterivorous protists. These results demonstrate a stable bottom-water microbial community. They also extend previous observations of food web-driven changes in euphotic zone bacterioplankton community structure to an oligotrophic setting. ?? 2007 Springer Science+Business Media B.V.

  11. Parasites in marine food webs

    USGS Publications Warehouse

    Lafferty, Kevin D.

    2013-01-01

    Most species interactions probably involve parasites. This review considers the extent to which marine ecologists should consider parasites to fully understand marine communities. Parasites are influential parts of food webs in estuaries, temperate reefs, and coral reefs, but their ecological importance is seldom recognized. Though difficult to observe, parasites can have substantial biomass, and they can be just as common as free-living consumers after controlling for body mass and trophic level. Parasites have direct impacts on the energetics of their hosts and some affect host behaviors, with ecosystem-level consequences. Although they cause disease, parasites are sensitive components of ecosystems. In particular, they suffer secondary extinctions due to biodiversity loss. Some parasites can also return to a system after habitat restoration. For these reasons, parasites can make good indicators of ecosystem integrity. Fishing can indirectly increase or decrease parasite populations and the effects of climate change on parasites are likely to be equally as complex.

  12. Impacts of changing food webs in Lake Ontario: Implications of dietary fatty acids on growth of alewives

    USGS Publications Warehouse

    Snyder, R.J.; Demarche, C.J.; Honeyfield, D.C.

    2011-01-01

    Declines in the abundance and condition of Great Lakes Alewives have been reported periodically during the last two decades, and the reasons for these declines remain unclear. To better understand how food web changes may influence Alewife growth and Wisconsin growth model predictions, we fed Alewives isocaloric diets high in omega-6 fatty acids (corn oil) or high in omega-3 fatty acids (fish oil). Alewives were fed the experimental diets at either 1% ("low ration") or 3% ("high ration") of their wet body weight per day. After six weeks, Alewives maintained on the high ration diets were significantly larger than those fed the low ration diets. Moreover, Alewives given the high ration fish oil diet were significantly larger than those maintained on the high ration corn oil diet after six weeks of growth. Body lipid, energy density and total body energy of Alewives on the high ration diets were significantly higher than those fed the low ration diets, and total body energy was significantly higher in Alewives given the high ration fish oil diet compared to those on the high ration corn oil diet. The current Wisconsin bioenergetics model underestimated growth and overestimated food consumption by Alewives in our study. Alewife thiaminase activity was similar among treatment groups. Overall, our results suggest that future food web changes in Lake Ontario, particularly if they involve decreases in the abundance of lipid rich prey items such as Mysis, may reduce Alewife growth rates and total body energy due to reductions in the availability of dietary omega-3 fatty acids. ?? 2011 AEHMS.

  13. Competition in di- and tri-trophic food web modules.

    PubMed

    Křivan, Vlastimil

    2014-02-21

    Competition in di- and tri-trophic food web modules with many competing species is studied. The food web modules considered are apparent competition between n species sharing a single predator and a diamond-like food web with a single resource, a single top predator and many competing middle species. The predators have either fixed preferences for their prey, or they switch between available prey in a way that maximizes their fitness. Dependence of these food web dynamics on environmental carrying capacity and food web connectance is studied. The results predict that optimal flexible foraging strongly weakens apparent competition and promotes species coexistence. Food web robustness (defined here as the proportion of surviving species) does not decrease with increased connectance in these food-webs. Moreover, it is shown that flexible prey switching leads to the same population equilibria as in corresponding food webs with highly specialized predators. The results show that flexible foraging behavior by predators can have very strong impact on species richness, as well as the response of communities to changes in resource enrichment and food-web connectance when compared to the same food-web topology with inflexible top predators. Several results on global stability using Lyapunov functions are provided.

  14. Insect symbionts in food webs

    PubMed Central

    Henry, Lee M.

    2016-01-01

    Recent research has shown that the bacterial endosymbionts of insects are abundant and diverse, and that they have numerous different effects on their hosts' biology. Here we explore how insect endosymbionts might affect the structure and dynamics of insect communities. Using the obligate and facultative symbionts of aphids as an example, we find that there are multiple ways that symbiont presence might affect food web structure. Many symbionts are now known to help their hosts escape or resist natural enemy attack, and others can allow their hosts to withstand abiotic stress or affect host plant use. In addition to the direct effect of symbionts on aphid phenotypes there may be indirect effects mediated through trophic and non-trophic community interactions. We believe that by using data from barcoding studies to identify bacterial symbionts, this extra, microbial dimension to insect food webs can be better elucidated. This article is part of the themed issue ‘From DNA barcodes to biomes’. PMID:27481779

  15. Future climate scenarios for a coastal productive planktonic food web resulting in microplankton phenology changes and decreased trophic transfer efficiency.

    PubMed

    Calbet, Albert; Sazhin, Andrey F; Nejstgaard, Jens C; Berger, Stella A; Tait, Zachary S; Olmos, Lorena; Sousoni, Despoina; Isari, Stamatina; Martínez, Rodrigo A; Bouquet, Jean-Marie; Thompson, Eric M; Båmstedt, Ulf; Jakobsen, Hans H

    2014-01-01

    We studied the effects of future climate change scenarios on plankton communities of a Norwegian fjord using a mesocosm approach. After the spring bloom, natural plankton were enclosed and treated in duplicates with inorganic nutrients elevated to pre-bloom conditions (N, P, Si; eutrophication), lowering of 0.4 pH units (acidification), and rising 3°C temperature (warming). All nutrient-amended treatments resulted in phytoplankton blooms dominated by chain-forming diatoms, and reached 13-16 μg chlorophyll (chl) a l-1. In the control mesocosms, chl a remained below 1 μg l-1. Acidification and warming had contrasting effects on the phenology and bloom-dynamics of autotrophic and heterotrophic microplankton. Bacillariophyceae, prymnesiophyceae, cryptophyta, and Protoperidinium spp. peaked earlier at higher temperature and lower pH. Chlorophyta showed lower peak abundances with acidification, but higher peak abundances with increased temperature. The peak magnitude of autotrophic dinophyceae and ciliates was, on the other hand, lowered with combined warming and acidification. Over time, the plankton communities shifted from autotrophic phytoplankton blooms to a more heterotrophic system in all mesocosms, especially in the control unaltered mesocosms. The development of mass balance and proportion of heterotrophic/autotrophic biomass predict a shift towards a more autotrophic community and less-efficient food web transfer when temperature, nutrients and acidification are combined in a future climate-change scenario. We suggest that this result may be related to a lower food quality for microzooplankton under acidification and warming scenarios and to an increase of catabolic processes compared to anabolic ones at higher temperatures.

  16. Progressive changes in the Western English Channel foster a reorganization in the plankton food web

    NASA Astrophysics Data System (ADS)

    Reygondeau, Gabriel; Molinero, Juan Carlos; Coombs, Steve; MacKenzie, Brian R.; Bonnet, Delphine

    2015-09-01

    Growing evidence has shown a profound modification of plankton communities of the North East Atlantic and adjacent seas over the past decades. This drastic change has been attributed to a modification of the environmental conditions that regulate the dynamics and the spatial distribution of ectothermic species in the ocean. Recently, several studies have highlighted modifications of the regional climate station L4 (50° 15.00‧N, 4° 13.02‧W) in the Western English Channel. We here focus on the modification of the plankton community by studying the long-term, annual and seasonal changes of five zooplankton groups and eight copepod genera. We detail the main composition and the phenology of the plankton communities during four climatic periods identified at the L4 station: 1988-1994, 1995-2000, 2001-2007 and 2008-2012. Our results show that long-term environmental changes underlined by Molinero et al. (2013) drive a profound restructuration of the plankton community modifying the phenology and the dominance of key planktonic groups including fish larvae. Consequently, the slow but deep modifications detected in the plankton community highlight a climate driven ecosystem shift in the Western English Channel.

  17. Source food webs as estimators of community web structure

    NASA Astrophysics Data System (ADS)

    Hawkins, Bradford A.; Martinez, Neo D.; Gilbert, Francis

    Taxonomically restricted "source webs" are commonly used to represent the community food webs of which they are part. This raises a methodological problem if source webs provide biased estimates of food web structure. We use four high quality, extensive food webs containing multiple source species to measure the sensitivity of food web metrics to the number of source species used to generate a web. The total number of species ( S), linkage density ( L/S), directed connectance ( L/S 2) and the fractions of basal ( B), intermediate ( I), and top ( T) species are all sensitive to the number of source species. Further, the pattern of variation for the latter fractions is inconsistent and web dependent, indicating that source webs are inappropriate for characterizing these properties. Linkage densities increase with the numbers of source species in all four cases, with webs based on single or few sources severely underestimating values obtained for the full webs. Connectance shows more constrained decreases with increasing numbers of sources, suggesting that multiple-source webs may provide reasonable estimates of connectance for community webs.

  18. Where are the parasites in food webs?

    PubMed Central

    2012-01-01

    This review explores some of the reasons why food webs seem to contain relatively few parasite species when compared to the full diversity of free living species in the system. At present, there are few coherent food web theories to guide scientific studies on parasites, and this review posits that the methods, directions and questions in the field of food web ecology are not always congruent with parasitological inquiry. For example, topological analysis (the primary tool in food web studies) focuses on only one of six important steps in trematode life cycles, each of which requires a stable community dynamic to evolve. In addition, these transmission strategies may also utilize pathways within the food web that are not considered in traditional food web investigations. It is asserted that more effort must be focused on parasite-centric models, and a central theme is that many different approaches will be required. One promising approach is the old energetic perspective, which considers energy as the critical resource for all organisms, and the currency of all food web interactions. From the parasitological point of view, energy can be used to characterize the roles of parasites at all levels in the food web, from individuals to populations to community. The literature on parasite energetics in food webs is very sparse, but the evidence suggests that parasite species richness is low in food webs because parasites are limited by the quantity of energy available to their unique lifestyles. PMID:23092160

  19. Lake Ontario: Food web dynamics in a changing ecosystem (1970-2000)

    USGS Publications Warehouse

    Mills, E.L.; Casselman, J.M.; Dermott, R.; Fitzsimons, J.D.; Gal, G.; Holeck, K. T.; Hoyle, J.A.; Johannsson, O.E.; Lantry, B.F.; Makarewicz, J.C.; Millard, E.S.; Munawar, I.F.; Munawar, M.; O'Gorman, R.; Owens, R.W.; Rudstam, L. G.; Schaner, T.; Stewart, T.J.

    2003-01-01

    We examined stressors that have led to profound ecological changes in the Lake Ontario ecosystem and its fish community since 1970. The most notable changes have been reductions in phosphorus loading, invasion by Dreissena spp., fisheries management through stocking of exotic salmonids and control of sea lamprey (Petromyzon marinus), and fish harvest by anglers and double-crested cormorants (Phalacrocorax auritus). The response to these stressors has led to (i) declines in both algal photosynthesis and epilimnetic zooplankton production, (ii) decreases in alewife (Alosa pseudoharengus) abundance, (iii) declines in native Diporeia and lake whitefish (Coregonus clupeaformis), (iv) behavioral shifts in alewife spatial distribution benefitting native lake trout (Salvelinus namaycush), threespine stickleback (Gasterosteus aculeatus), and emerald shiner (Notropis atherinoides) populations, (v) dramatic increases in water clarity, (vi) predation impacts by cormorants on select fish species, and (vii) lake trout recruitment bottlenecks associated with alewife-induced thiamine deficiency. We expect stressor responses associated with anthropogenic forces like exotic species invasions and global climate warming to continue to impact the Lake Ontario ecosystem in the future and recommend continuous long-term ecological studies to enhance scientific understanding and management of this important resource.

  20. Drought rewires the cores of food webs

    NASA Astrophysics Data System (ADS)

    Lu, Xueke; Gray, Clare; Brown, Lee E.; Ledger, Mark E.; Milner, Alexander M.; Mondragón, Raúl J.; Woodward, Guy; Ma, Athen

    2016-09-01

    Droughts are intensifying across the globe, with potentially devastating implications for freshwater ecosystems. We used new network science approaches to investigate drought impacts on stream food webs and explored potential consequences for web robustness to future perturbations. The substructure of the webs was characterized by a core of richly connected species surrounded by poorly connected peripheral species. Although drought caused the partial collapse of the food webs, the loss of the most extinction-prone peripheral species triggered a substantial rewiring of interactions within the networks’ cores. These shifts in species interactions in the core conserved the underlying core/periphery substructure and stability of the drought-impacted webs. When we subsequently perturbed the webs by simulating species loss in silico, the rewired drought webs were as robust as the larger, undisturbed webs. Our research unearths previously unknown compensatory dynamics arising from within the core that could underpin food web stability in the face of environmental perturbations.

  1. Food web persistence is enhanced by non-trophic interactions.

    PubMed

    Hammill, Edd; Kratina, Pavel; Vos, Matthijs; Petchey, Owen L; Anholt, Bradley R

    2015-06-01

    The strength of interspecific interactions is often proposed to affect food web stability, with weaker interactions increasing the persistence of species, and food webs as a whole. However, the mechanisms that modify interaction strengths, and their effects on food web persistence are not fully understood. Using food webs containing different combinations of predator, prey, and nonprey species, we investigated how predation risk of susceptible prey is affected by the presence of species not directly trophically linked to either predators or prey. We predicted that indirect alterations to the strength of trophic interactions translate to changes in persistence time of extinction-prone species. We assembled interaction webs of protist consumers and turbellarian predators with eight different combinations of prey, predators and nonprey species, and recorded abundances for over 130 prey generations. Persistence of predation-susceptible species was increased by the presence of nonprey. Furthermore, multiple nonprey species acted synergistically to increase prey persistence, such that persistence was greater than would be predicted from the dynamics of simpler food webs. We also found evidence suggesting increased food web complexity may weaken interspecific competition, increasing persistence of poorer competitors. Our results demonstrate that persistence times in complex food webs cannot be predicted from the dynamics of simplified systems, and that species not directly involved in consumptive interactions likely play key roles in maintaining persistence. Global species diversity is currently declining at an unprecedented rate and our findings reveal that concurrent loss of species that modify trophic interactions may have unpredictable consequences for food web stability.

  2. Food web complexity and stability across habitat connectivity gradients.

    PubMed

    LeCraw, Robin M; Kratina, Pavel; Srivastava, Diane S

    2014-12-01

    The effects of habitat connectivity on food webs have been studied both empirically and theoretically, yet the question of whether empirical results support theoretical predictions for any food web metric other than species richness has received little attention. Our synthesis brings together theory and empirical evidence for how habitat connectivity affects both food web stability and complexity. Food web stability is often predicted to be greatest at intermediate levels of connectivity, representing a compromise between the stabilizing effects of dispersal via rescue effects and prey switching, and the destabilizing effects of dispersal via regional synchronization of population dynamics. Empirical studies of food web stability generally support both this pattern and underlying mechanisms. Food chain length has been predicted to have both increasing and unimodal relationships with connectivity as a result of predators being constrained by the patch occupancy of their prey. Although both patterns have been documented empirically, the underlying mechanisms may differ from those predicted by models. In terms of other measures of food web complexity, habitat connectivity has been empirically found to generally increase link density but either reduce or have no effect on connectance, whereas a unimodal relationship is expected. In general, there is growing concordance between empirical patterns and theoretical predictions for some effects of habitat connectivity on food webs, but many predictions remain to be tested over a full connectivity gradient, and empirical metrics of complexity are rarely modeled. Closing these gaps will allow a deeper understanding of how natural and anthropogenic changes in connectivity can affect real food webs.

  3. Food-web dynamics in a large river discontinuum

    USGS Publications Warehouse

    Cross, Wyatt F.; Baxter, Colden V.; Rosi-Marshall, Emma J.; Hall, Robert O.; Kennedy, Theodore A.; Donner, Kevin C.; Kelly, Holly A. Wellard; Seegert, Sarah E.Z.; Behn, Kathrine E.; Yard, Michael D.

    2013-01-01

    Nearly all ecosystems have been altered by human activities, and most communities are now composed of interacting species that have not co-evolved. These changes may modify species interactions, energy and material flows, and food-web stability. Although structural changes to ecosystems have been widely reported, few studies have linked such changes to dynamic food-web attributes and patterns of energy flow. Moreover, there have been few tests of food-web stability theory in highly disturbed and intensely managed freshwater ecosystems. Such synthetic approaches are needed for predicting the future trajectory of ecosystems, including how they may respond to natural or anthropogenic perturbations. We constructed flow food webs at six locations along a 386-km segment of the Colorado River in Grand Canyon (Arizona, USA) for three years. We characterized food-web structure and production, trophic basis of production, energy efficiencies, and interaction-strength distributions across a spatial gradient of perturbation (i.e., distance from Glen Canyon Dam), as well as before and after an experimental flood. We found strong longitudinal patterns in food-web characteristics that strongly correlated with the spatial position of large tributaries. Above tributaries, food webs were dominated by nonnative New Zealand mudsnails (62% of production) and nonnative rainbow trout (100% of fish production). The simple structure of these food webs led to few dominant energy pathways (diatoms to few invertebrate taxa to rainbow trout), large energy inefficiencies (i.e., Below large tributaries, invertebrate production declined ∼18-fold, while fish production remained similar to upstream sites and comprised predominately native taxa (80–100% of production). Sites below large tributaries had increasingly reticulate and detritus-based food webs with a higher prevalence of omnivory, as well as interaction strength distributions more typical of theoretically stable food webs (i

  4. Food web and fish stock changes in central Chile: comparing the roles of jumbo squid (Dosidicus gigas) predation, the environment, and fisheries

    NASA Astrophysics Data System (ADS)

    Neira, Sergio; Arancibia, Hugo

    2013-10-01

    We analyzed recent food web and fish stock changes in the central Chile marine ecosystem, comparing the roles of jumbo squid (Dosidicus gigas) as predator, the environment, and fishing. To accomplish this we used food web modeling and the Ecopath with Ecosim software (EwE). The principal fish stocks have experienced wide decadal fluctuations in the past 30 years, including stock collapses of horse mackerel (Trachurus murphyi) and hake (Merluccius gayi), and there was a large influx of jumbo squid during the mid-2000s. We used two EwE models representing the food web off central Chile to test the hypothesis that predation by jumbo squid has been significant in explaining the dynamics of the main fishing resources and other species in the study area. Results indicate that predation by jumbo squid on fish stocks is lower than that of other predators (e.g. hake) and the fishery. Long-term fluctuations (1978-2004) in the biomass of the main fish stocks (as well as other components of the food web) seem to be related to fishing and to variation in primary production, rather than to predation by jumbo squid alone. Jumbo squid seems to play a role as predator rather than prey in the system, but its impacts are low when compared with the impacts of other predators and fishing. Therefore, we conclude that jumbo squid predation on its prey was not the primary force behind the collapse of important fish stocks off central Chile. Future efforts should be directed to better understanding factors that trigger sudden increases in jumbo squid abundance off central Chile, as well as modeling its trophic impacts.

  5. An Ecosystem Approach for understanding status and changes of Nador lagoon (Morocco): application for of food web models and ecosystem indices

    NASA Astrophysics Data System (ADS)

    Bocci, M.; Brigolin, D.; Pranovi, F.; Najih, M.; Nachite, D.; Pastres, R.

    2016-03-01

    The work applies food web models to the Lagoon of Nador (Morocco) and subsequently estimates ecosystem indices. This effort supports the evaluation of the ecosystem status and the implementation of the Ecosystem Approach (EcAp), endorsed by the contracting parties of the Barcelona Convention for the Mediterranean Sea. The Lagoon of Nador, on the Mediterranean coast of Morocco, suffered from eutrophication during recent decades. We used indices derived from Ecological Network Analysis for investigating the most relevant features of ecosystem functioning in the decade 2000-2010 (present scenario), and comparing them with those of the 1980s (past scenario). As the Lagoon includes different habitats, the methodology was applied to each of them, in order to assess their contribution to the functioning of the whole ecosystem. Results highlighted an increase in Total System Throughput (TST) in the present scenario when compared with the past one, also associated to an increase of Total Respiration (TR) and of the ratio between Total Primary Production and Total Respiration (TPP/TR). Under the present scenario Nador lagoon shows a decreased cycling efficiency. The sensitivity analysis highlighted the capability of TST and Comprehensive Cycling Index (CCI) in detecting changes, in agreement with other recent studies on responses of food web functioning to eutrophication. The results are discussed in respect to three specific aspects, related with the application of food Web Models and Ecological Network Analysis in the EcAp context: i) data availability; ii) spatialization of indicators; iii) selected set of indicators. The results also highlight the important role of sensitivity/uncertainty analysis when implementing food web models in data-scarce systems.

  6. Adaptations in a hierarchical food web of southeastern Lake Michigan

    USGS Publications Warehouse

    Krause, Ann E.; Frank, Ken A.; Jones, Michael L.; Nalepa, Thomas F.; Barbiero, Richard P.; Madenjian, Charles P.; Agy, Megan; Evans, Marlene S.; Taylor, William W.; Mason, Doran M.; Leonard, Nancy J.

    2009-01-01

    Two issues in ecological network theory are: (1) how to construct an ecological network model and (2) how do entire networks (as opposed to individual species) adapt to changing conditions? We present a novel method for constructing an ecological network model for the food web of southeastern Lake Michigan (USA) and we identify changes in key system properties that are large relative to their uncertainty as this ecological network adapts from one time point to a second time point in response to multiple perturbations. To construct our food web for southeastern Lake Michigan, we followed the list of seven recommendations outlined in Cohen et al. [Cohen, J.E., et al., 1993. Improving food webs. Ecology 74, 252–258] for improving food webs. We explored two inter-related extensions of hierarchical system theory with our food web; the first one was that subsystems react to perturbations independently in the short-term and the second one was that a system's properties change at a slower rate than its subsystems’ properties. We used Shannon's equations to provide quantitative versions of the basic food web properties: number of prey, number of predators, number of feeding links, and connectance (or density). We then compared these properties between the two time-periods by developing distributions of each property for each time period that took uncertainty about the property into account. We compared these distributions, and concluded that non-overlapping distributions indicated changes in these properties that were large relative to their uncertainty. Two subsystems were identified within our food web system structure (p < 0.001). One subsystem had more non-overlapping distributions in food web properties between Time 1 and Time 2 than the other subsystem. The overall system had all overlapping distributions in food web properties between Time 1 and Time 2. These results supported both extensions of hierarchical systems theory. Interestingly, the subsystem with more

  7. Dining Dovekies Demand, "When, Where and What's for Dinner?" The Impact of Seasonal Changes in Snow Melt and the Development of the Arctic Marine Food Web on Seabirds.

    NASA Astrophysics Data System (ADS)

    Karnovsky, N. J.; Harding, A.; Welcker, J.; Brown, Z. W.; Kitaysky, A.; Kwasniewski, S.; Walkusz, W.; Gremillet, D.

    2011-12-01

    The Atlantic sector of the Arctic is undergoing widespread climate change with increases in air and sea temperatures which impact the timing of ice retreat, snow melt and the development of the marine food web. Dovekies (Alle alle) are small seabirds that migrate to the Atlantic Sector of the Arctic to feed in ice free waters that have abundant lipid-rich zooplankton. In the Greenland Sea, the dovekies are largely dependent on the advection of Calanus copepods into the area. We hypothesized that dovekies breeding adjacent to water masses which bring smaller, less energy-rich prey into the region (Calanus finmarchicus), work harder to find food and have higher stress levels. We tested this hypothesis by attaching time-depth recorders to provisioning dovekies at three colonies adjacent to different water masses (the West Spistbergen Current, the East Greenland Current, and the Sorkapp Current). We determined the length of time dovekies at different colonies spent at-sea collecting food for themselves and their chicks. We measured circulating corticosteroid hormone levels in their blood to assess stress levels. We collected chick meals to determine the energetic content of prey fed chicks at the different colonies. We found that dovekies are sensitive to the quality of prey available to them. Dovekies exposed to less profitable prey made longer foraging trips and worked harder while at-sea to collect prey for themselves and their chicks. Furthermore, over the past 50 years, dovekies breeding along the western shores of Spitsbergen have initiated breeding earlier in spring as their nest sites have become snow-free at earlier dates. We evaluate the impact of earlier breeding and the timing of the development of the marine food web within different currents which advect and/or support Calanus copepods into the Greenland Sea. Future possible declines in dovekies may impact terrestrial food webs which are highly influenced by the annual input of nitrogen rich guano on the

  8. Effects of climate change on bioaccumulation and biomagnification of polycyclic aromatic hydrocarbons in the planktonic food web of a subtropical shallow eutrophic lake in China.

    PubMed

    Tao, Yuqiang; Xue, Bin; Lei, Guoliang; Liu, Fei; Wang, Zhen

    2017-04-01

    To date effects of climate change on bioaccumulation and biomagnification of chemical pollutants in planktonic food webs have rarely been studied. Recruitments of plankton have shifted earlier due to global warming. Global warming and precipitation patterns are projected to shift seasonally. Whether and how the shifts in plankton phenology induced by climate change will impact bioaccumulation and biomagnification of chemical pollutants, and how they will respond to climate change are largely unknown. Here, we combine data analysis of the past seven decades, high temporal resolution monitoring and model development to test this hypothesis with nine polycyclic aromatic hydrocarbons (PAHs) in the planktonic food web of a subtropical shallow eutrophic lake in China. We find biphasic correlations between both bioconcentration factors and bioaccumulation factors of the PAHs and the mean temperature, which depend on the recruitment temperatures of cyanobacteria, and copepods and cladocerans. The positive correlations between bioconcentration factors, bioaccumulation factors and the mean temperature will be observed less than approximately 13-18 days by 2050-2060 due to the shifts in plankton phenology. The PAHs and their bioaccumulation and biomagnification will respond seasonally and differently to climate change. Bioaccumulation of most of the PAHs will decrease with global warming, with higher decreasing rates appearing in winter and spring. Biomagnification of most of the PAHs from phytoplankton to zooplankton will increase with global warming, with higher increasing rates appearing in winter and spring. Our study provides novel insights into bioaccumulation and biomagnification of chemical pollutants in eutrophic waters under climate change scenarios.

  9. A robust measure of food web intervality

    PubMed Central

    Stouffer, Daniel B.; Camacho, Juan; Amaral, Luís A. Nunes

    2006-01-01

    Intervality of a food web is related to the number of trophic dimensions characterizing the niches in a community. We introduce here a mathematically robust measure for food web intervality. It has previously been noted that empirical food webs are not strictly interval; however, upon comparison to suitable null hypotheses, we conclude that empirical food webs actually do exhibit a strong bias toward contiguity of prey, that is, toward intervality. Further, our results strongly suggest that empirically observed species and their diets can be mapped onto a single dimension. This finding validates a critical assumption in the recently proposed static niche model and provides guidance for ongoing efforts to develop dynamic models of ecosystems. PMID:17146055

  10. Exposing the structure of an Arctic food web.

    PubMed

    Wirta, Helena K; Vesterinen, Eero J; Hambäck, Peter A; Weingartner, Elisabeth; Rasmussen, Claus; Reneerkens, Jeroen; Schmidt, Niels M; Gilg, Olivier; Roslin, Tomas

    2015-09-01

    How food webs are structured has major implications for their stability and dynamics. While poorly studied to date, arctic food webs are commonly assumed to be simple in structure, with few links per species. If this is the case, then different parts of the web may be weakly connected to each other, with populations and species united by only a low number of links. We provide the first highly resolved description of trophic link structure for a large part of a high-arctic food web. For this purpose, we apply a combination of recent techniques to describing the links between three predator guilds (insectivorous birds, spiders, and lepidopteran parasitoids) and their two dominant prey orders (Diptera and Lepidoptera). The resultant web shows a dense link structure and no compartmentalization or modularity across the three predator guilds. Thus, both individual predators and predator guilds tap heavily into the prey community of each other, offering versatile scope for indirect interactions across different parts of the web. The current description of a first but single arctic web may serve as a benchmark toward which to gauge future webs resolved by similar techniques. Targeting an unusual breadth of predator guilds, and relying on techniques with a high resolution, it suggests that species in this web are closely connected. Thus, our findings call for similar explorations of link structure across multiple guilds in both arctic and other webs. From an applied perspective, our description of an arctic web suggests new avenues for understanding how arctic food webs are built and function and of how they respond to current climate change. It suggests that to comprehend the community-level consequences of rapid arctic warming, we should turn from analyses of populations, population pairs, and isolated predator-prey interactions to considering the full set of interacting species.

  11. Does temporal variation of mercury levels in Arctic seabirds reflect changes in global environmental contamination, or a modification of Arctic marine food web functioning?

    PubMed

    Fort, Jérôme; Grémillet, David; Traisnel, Gwendoline; Amélineau, Françoise; Bustamante, Paco

    2016-04-01

    Studying long-term trends of contaminants in Arctic biota is essential to better understand impacts of anthropogenic activities and climate change on the exposure of sensitive species and marine ecosystems. We concurrently measured temporal changes (2006-2014) in mercury (Hg) contamination of little auks (Alle alle; the most abundant Arctic seabird) and in their major zooplankton prey species (Calanoid copepods, Themisto libellula, Gammarus spp.). We found an increasing contamination of the food-chain in East Greenland during summer over the last decade. More specifically, bird contamination (determined by body feather analyses) has increased at a rate of 3.4% per year. Conversely, bird exposure to Hg during winter in the northwest Atlantic (determined by head feather analyses) decreased over the study period (at a rate of 1.5% per year), although winter concentrations remained consistently higher than during summer. By combining mercury levels measured in birds and zooplankton to isotopic analyses, our results demonstrate that inter-annual variations of Hg levels in little auks reflect changes in food-chain contamination, rather than a reorganization of the food web and a modification of seabird trophic ecology. They therefore underline the value of little auks, and Arctic seabirds in general, as bio-indicators of long-term changes in environmental contamination.

  12. Soil processes and tree growth at shooting ranges in a boreal forest reflect contamination history and lead-induced changes in soil food webs.

    PubMed

    Selonen, Salla; Setälä, Heikki

    2015-06-15

    The effects of shooting-derived lead (Pb) on the structure and functioning of a forest ecosystem, and the recovery of the ecosystem after range abandonment were studied at an active shotgun shooting range, an abandoned shooting range where shooting ceased 20 years earlier and an uncontaminated control site. Despite numerous lead-induced changes in the soil food web, soil processes were only weakly related to soil food web composition. However, decomposition of Scots pine (Pinus sylvestris) needle litter was retarded at the active shooting range, and microbial activity, microbial biomass and the rate of decomposition of Pb-contaminated grass litter decreased with increasing soil Pb concentrations. Tree (P. sylvestris) radial growth was suppressed at the active shooting range right after shooting activities started. In contrast, the growth of pines improved at the abandoned shooting range after the cessation of shooting, despite reduced nitrogen and phosphorus contents of the needles. Higher litter degradation rates and lower Pb concentrations in the topmost soil layer at the abandoned shooting range suggest gradual recovery after range abandonment. Our findings suggest that functions in lead-contaminated coniferous forest ecosystems depend on the successional stage of the forest as well as the time since the contamination source has been eliminated, which affects, e.g., the vertical distribution of the contaminant in the soil. However, despite multiple lead-induced changes throughout the ecosystem, the effects were rather weak, indicating high resistance of coniferous forest ecosystems to this type of stress.

  13. Food Chain to Food Web: A Natural Progression?

    ERIC Educational Resources Information Center

    Webb, Paul; Boltt, Gill

    1990-01-01

    Investigated is the ability of high school pupils and university students to answer questions based on relationships within food webs using sound ecological principles. Research methods used and the results of this study are discussed. (CW)

  14. Inducible defenses in food webs: Chapter 3.4

    USGS Publications Warehouse

    Vos, Matthijs; Kooi, Bob W.; DeAngelis, Donald L.; Mooij, Wolf M.; de Ruiter, Peter; Wolters, Volkmar; Moore, John C.; Melville-Smith, Kimberly

    2005-01-01

    This chapter reviews the predicted effects of induced defenses on trophic structure and two aspects of stability, “local” stability and persistence, as well as presenting novel results on a third, resilience. Food webs are structures of populations in a given location organized according to their predator–prey interactions. Interaction strengths and, therefore, prey defenses are generally recognized as important ecological factors affecting food webs. Despite this, surprisingly, little light has been shed on the food web-level consequences of inducible defenses. Inducible defenses occur in many taxa in both terrestrial and aquatic food webs. They include refuge use, reduced activity, adaptive life history changes, the production of toxins, synomones and extrafloral nectar, and the formation of colonies, helmets, thorns, or spines. In the chapter, theoretical results for the effects of inducible defenses on trophic structure and the three aspects of stability are reviewed. This is done, in part, using bifurcation analysis—a type of analysis that is applied to nonlinear dynamic systems described by a set of ordinary differential or difference equations. The work presented in the chapter suggests that heterogeneity, as caused by induced defenses in prey species, has major effects on the functioning of food webs. Inducible defenses occur in many species in both aquatic and terrestrial systems, and theoretical work indicates they have major effects on important food web properties such as trophic structure, local stability, persistence, and resilience.

  15. Barcoding a quantified food web: crypsis, concepts, ecology and hypotheses.

    PubMed

    Smith, M Alex; Eveleigh, Eldon S; McCann, Kevin S; Merilo, Mark T; McCarthy, Peter C; Van Rooyen, Kathleen I

    2011-01-01

    outbreaks. Integrating standardized barcodes within food webs may ultimately change the face of community ecology. This will be most poignantly felt in food webs that have not yet been quantified. Here, more accurate and precise connections will be within the grasp of any researcher for the first time.

  16. Climate driven changes in hydrology, nutrient cycling, and food web dynamics in surface waters of the Arctic Coastal Plain, Alaska

    NASA Astrophysics Data System (ADS)

    Koch, J. C.; Wipfli, M.; Schmutz, J.; Gurney, K.

    2011-12-01

    Arctic ecosystems are changing rapidly as a result of a warming climate. While many areas of the arctic are expected to dry as a result of warming, the Arctic Coastal Plain (ACP) of Alaska, which extends from the Brooks Range north to the Beaufort Sea will likely become wetter, because subsurface hydrologic fluxes are constrained by thick, continuous permafrost. This landscape is characterized by large, oriented lakes and many smaller ponds that form in the low centers and troughs/edges of frost polygons. This region provides important breeding habitat for many migratory birds including loons, arctic terns, eiders, shorebirds, and white-fronted geese, among others. Increased hydrologic fluxes may provide a bottom-up control on the success of these species by altering the availability of food resources including invertebrates and fish. This work aimed to 1) characterize surface water fluxes and nutrient availability in the small streams and lake types of two study regions in the ACP, 2) predict how increased hydrological fluxes will affect the lakes, streams, and water chemistry, and 3) use nutrient additions to simulate likely changes in lake chemistry and invertebrate availability. Initial observations suggest that increasing wetland areas and availability of nutrients will result in increased invertebrate abundance, while the potential for drainage and terrestrialization of larger lakes may reduce fish abundance and overwintering habitat. These changes will likely have positive implications for insectivores and negative implications for piscivorous waterfowl.

  17. Nutrient dynamics and food-web stability

    SciTech Connect

    DeAngelis, D.L.; Mulholland, P.J.; Palumbo, A.V.; Steinman, A.D.; Huston, M.A.; Elwood, J.W. )

    1989-01-01

    The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships. What are the effects of limiting nutrients on the stability of ecosystem food webs Most of the literature on food web stability centers around the dynamics of population numbers and/or biomasses. Nevertheless, a growing body of theoretical and empirical research considers the role that both nutrient limitation and recycling can play in stability. In this paper, it is the authors objective to summarize the current understanding of several important types of stability. The theoretical and empirical evidence relating these types of stability and nutrient cycling is described. A central generalization is produced in each case.

  18. Food terrorism and food defense on the Web.

    PubMed

    Taylor, Mary Kay

    2008-01-01

    Global food supplies are at risk of both accidental and deliberate contamination. As past incidents have demonstrated, food terrorism may cause social, economic, and political disruption. The United States increased its efforts to protect its food after 9/11 by broadening the roles of existing agencies, including the U.S. Department of Agriculture and the Food and Drug Administration, and by making coordination of food defense the responsibility of the Department of Homeland Security. However, weaknesses in the system remain. This article presents background information and Web sites useful for consumers, industry representatives, students, researchers, policy makers, and the librarians that serve them.

  19. Environmental controls on food web regimes: A fluvial perspective

    NASA Astrophysics Data System (ADS)

    Power, Mary E.

    2006-02-01

    Because food web regimes control the biomass of primary producers (e.g., plants or algae), intermediate consumers (e.g., invertebrates), and large top predators (tuna, killer whales), they are of societal as well as academic interest. Some controls over food web regimes may be internal, but many are mediated by conditions or fluxes over large spatial scales. To understand locally observed changes in food webs, we must learn more about how environmental gradients and boundaries affect the fluxes of energy, materials, or organisms through landscapes or seascapes that influence local species interactions. Marine biologists and oceanographers have overcome formidable challenges of fieldwork on the high seas to make remarkable progress towards this goal. In river drainage networks, we have opportunities to address similar questions at smaller spatial scales, in ecosystems with clear physical structure and organization. Despite these advantages, we still have much to learn about linkages between fluxes from watershed landscapes and local food webs in river networks. Longitudinal (downstream) gradients in productivity, disturbance regimes, and habitat structure exert strong effects on the organisms and energy sources of river food webs, but their effects on species interactions are just beginning to be explored. In fluid ecosystems with less obvious physical structure, like the open ocean, discerning features that control the movement of organisms and affect food web dynamics is even more challenging. In both habitats, new sensing, tracing and mapping technologies have revealed how landscape or seascape features (e.g., watershed divides, ocean fronts or circulation cells) channel, contain or concentrate organisms, energy and materials. Field experiments and direct in situ observations of basic natural history, however, remain as vital as ever in interpreting the responses of biota to these features. We need field data that quantify the many spatial and temporal scales of

  20. Food-web stability signals critical transitions in temperate shallow lakes.

    PubMed

    Kuiper, Jan J; van Altena, Cassandra; de Ruiter, Peter C; van Gerven, Luuk P A; Janse, Jan H; Mooij, Wolf M

    2015-07-15

    A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it is unclear how the concept of food-web stability is associated with the resilience of ecosystems susceptible to regime change. Here, we use a combination of food web and ecosystem modelling to show that impending catastrophic shifts in shallow lakes are preceded by a destabilizing reorganization of interaction strengths in the aquatic food web. Analysis of the intricate web of trophic interactions reveals that only few key interactions, involving zooplankton, diatoms and detritus, dictate the deterioration of food-web stability. Our study exposes a tight link between food-web dynamics and the dynamics of the whole ecosystem, implying that trophic organization may serve as an empirical indicator of ecosystem resilience.

  1. Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts

    PubMed Central

    Coll, Marta; Schmidt, Allison; Romanuk, Tamara; Lotze, Heike K.

    2011-01-01

    Seagrass beds provide important habitat for a wide range of marine species but are threatened by multiple human impacts in coastal waters. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. Motivated by extensive field surveys and literature information, we analyzed the structural features of food webs associated with Zostera marina across 16 study sites in 3 provinces in Atlantic Canada. Our goals were to (i) quantify differences in food-web structure across local and regional scales and human impacts, (ii) assess the robustness of seagrass webs to simulated species loss, and (iii) compare food-web structure in temperate Atlantic seagrass beds with those of other aquatic ecosystems. We constructed individual food webs for each study site and cumulative webs for each province and the entire region based on presence/absence of species, and calculated 16 structural properties for each web. Our results indicate that food-web structure was similar among low impact sites across regions. With increasing human impacts associated with eutrophication, however, food-web structure show evidence of degradation as indicated by fewer trophic groups, lower maximum trophic level of the highest top predator, fewer trophic links connecting top to basal species, higher fractions of herbivores and intermediate consumers, and higher number of prey per species. These structural changes translate into functional changes with impacted sites being less robust to simulated species loss. Temperate Atlantic seagrass webs are similar to a tropical seagrass web, yet differed from other aquatic webs, suggesting consistent food-web characteristics across seagrass ecosystems in different regions. Our study illustrates that food-web structure and functioning of seagrass habitats change with human impacts and that the spatial scale of food-web analysis

  2. Food-web structure of seagrass communities across different spatial scales and human impacts.

    PubMed

    Coll, Marta; Schmidt, Allison; Romanuk, Tamara; Lotze, Heike K

    2011-01-01

    Seagrass beds provide important habitat for a wide range of marine species but are threatened by multiple human impacts in coastal waters. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. Motivated by extensive field surveys and literature information, we analyzed the structural features of food webs associated with Zostera marina across 16 study sites in 3 provinces in Atlantic Canada. Our goals were to (i) quantify differences in food-web structure across local and regional scales and human impacts, (ii) assess the robustness of seagrass webs to simulated species loss, and (iii) compare food-web structure in temperate Atlantic seagrass beds with those of other aquatic ecosystems. We constructed individual food webs for each study site and cumulative webs for each province and the entire region based on presence/absence of species, and calculated 16 structural properties for each web. Our results indicate that food-web structure was similar among low impact sites across regions. With increasing human impacts associated with eutrophication, however, food-web structure show evidence of degradation as indicated by fewer trophic groups, lower maximum trophic level of the highest top predator, fewer trophic links connecting top to basal species, higher fractions of herbivores and intermediate consumers, and higher number of prey per species. These structural changes translate into functional changes with impacted sites being less robust to simulated species loss. Temperate Atlantic seagrass webs are similar to a tropical seagrass web, yet differed from other aquatic webs, suggesting consistent food-web characteristics across seagrass ecosystems in different regions. Our study illustrates that food-web structure and functioning of seagrass habitats change with human impacts and that the spatial scale of food-web analysis

  3. IsoWeb: a bayesian isotope mixing model for diet analysis of the whole food web.

    PubMed

    Kadoya, Taku; Osada, Yutaka; Takimoto, Gaku

    2012-01-01

    Quantitative description of food webs provides fundamental information for the understanding of population, community, and ecosystem dynamics. Recently, stable isotope mixing models have been widely used to quantify dietary proportions of different food resources to a focal consumer. Here we propose a novel mixing model (IsoWeb) that estimates diet proportions of all consumers in a food web based on stable isotope information. IsoWeb requires a topological description of a food web, and stable isotope signatures of all consumers and resources in the web. A merit of IsoWeb is that it takes into account variation in trophic enrichment factors among different consumer-resource links. Sensitivity analysis using realistic hypothetical food webs suggests that IsoWeb is applicable to a wide variety of food webs differing in the number of species, connectance, sample size, and data variability. Sensitivity analysis based on real topological webs showed that IsoWeb can allow for a certain level of topological uncertainty in target food webs, including erroneously assuming false links, omission of existent links and species, and trophic aggregation into trophospecies. Moreover, using an illustrative application to a real food web, we demonstrated that IsoWeb can compare the plausibility of different candidate topologies for a focal web. These results suggest that IsoWeb provides a powerful tool to analyze food-web structure from stable isotope data. We provide R and BUGS codes to aid efficient applications of IsoWeb.

  4. Benthic Food Webs of the Chukchi and Beaufort Seas: Relative Importance of Ultimate Carbon Sources in a Changing Climate

    NASA Astrophysics Data System (ADS)

    Dunton, K. H.; Schonberg, S. V.; Mctigue, N.; Bucolo, P. A.; Connelly, T. L.; McClelland, J. W.

    2014-12-01

    Changes in sea-ice cover, coastal erosion, and freshwater run-off have the potential to greatly influence carbon assimilation pathways and affect trophic structure in benthic communities across the western Arctic. In the Chukchi Sea, variations in the duration and timing of ice cover affect the delivery of ice algae to a relatively shallow (40-50 m) shelf benthos. Although ice algae are known as an important spring carbon subsidy for marine benthic fauna, ice algal contributions may also help initiate productivity of an active microphytobenthos. Recent studies provide clear evidence that the microphytobenthos are photosynthetically active, and have sufficient light and nutrients for in situ growth. The assimilation of benthic diatoms from both sources may explain the 13C enrichment observed in benthic primary consumers throughout the northern Chukchi. On the eastern Beaufort Sea coast, shallow (2-4 m) estuarine lagoon systems receive massive subsidies of terrestrial carbon that is assimilated by a benthic fauna of significant importance to upper trophic level species, but again, distinct 13C enrichment in benthic primary consumers suggests the existence of an uncharacterized food source. Since ice algae are absent, we believe the 13C enrichment in benthic fauna is caused by the assimilation of benthic microalgae, as reflected in seasonally high benthic chlorophyll in spring under replete light and nutrient conditions. Our observations suggest that changes in ice cover, on both temporal and spatial scales, are likely to have significant effects on the magnitude and timing of organic matter delivery to both shelf and nearshore systems, and that locally produced organic matter may become an increasingly important carbon subsidy that affects trophic assimilation and secondary ecosystem productivity.

  5. Linking structure and function in food webs: maximization of different ecological functions generates distinct food web structures.

    PubMed

    Yen, Jian D L; Cabral, Reniel B; Cantor, Mauricio; Hatton, Ian; Kortsch, Susanne; Patrício, Joana; Yamamichi, Masato

    2016-03-01

    Trophic interactions are central to ecosystem functioning, but the link between food web structure and ecosystem functioning remains obscure. Regularities (i.e. consistent patterns) in food web structure suggest the possibility of regularities in ecosystem functioning, which might be used to relate structure to function. We introduce a novel, genetic algorithm approach to simulate food webs with maximized throughput (a proxy for ecosystem functioning) and compare the structure of these simulated food webs to real empirical food webs using common metrics of food web structure. We repeat this analysis using robustness to secondary extinctions (a proxy for ecosystem resilience) instead of throughput to determine the relative contributions of ecosystem functioning and ecosystem resilience to food web structure. Simulated food webs that maximized robustness were similar to real food webs when connectance (i.e. levels of interaction across the food web) was high, but this result did not extend to food webs with low connectance. Simulated food webs that maximized throughput or a combination of throughput and robustness were not similar to any real food webs. Simulated maximum-throughput food webs differed markedly from maximum-robustness food webs, which suggests that maximizing different ecological functions can generate distinct food web structures. Based on our results, food web structure would appear to have a stronger relationship with ecosystem resilience than with ecosystem throughput. Our genetic algorithm approach is general and is well suited to large, realistically complex food webs. Genetic algorithms can incorporate constraints on structure and can generate outputs that can be compared directly to empirical data. Our method can be used to explore a range of maximization or minimization hypotheses, providing new perspectives on the links between structure and function in ecological systems.

  6. Food Webs in an Estuary.

    ERIC Educational Resources Information Center

    Dunne, Barbara B.

    The Maryland Marine Science Education Project has produced a series of mini-units in marine science education for the junior high/middle school classroom. This unit focuses on food chains in an estuary. Although the unit specifically treats the Chesapeake Bay, it may be adapted for use with similar estuarine systems. In addition, the unit may be…

  7. Priceless prices and marine food webs: Long-term patterns of change and fishing impacts in the South Brazil Bight as reflected by the seafood market

    NASA Astrophysics Data System (ADS)

    Pincinato, R. B. M.; Gasalla, M. A.

    2010-10-01

    The lack of market variables in fishery systems (i.e., prices and quantities) has often been cited as one reason for the particular difficulty of understanding whole marine ecosystem change and its management under a broader ecosystem perspective. This paper shows the results of efforts to tackle this problem in the South Brazil Bight by compiling and analyzing in-depth an unprecedented 40-year database from the region’s largest wholesale seafood market, based in the megacity of São Paulo. Fishery landings and market values for the period 1968-2007 were analyzed primarily by updated trophic level classes and multispecies indicators including the (1) marine trophic index (MTI), (2) weighted price, and (3) log relative price index (LRPI) which relates prices and trophic levels. Moreover, an inferential analysis of major seafood category statistical trends in market prices and quantities and their positive and negative correlations was undertaken. In general, these market trends contributed substantially to identifying and clarifying the changes that occurred. Considerations of the behavior of demand, supply and markets are included. In particular, while the MTI did not support a “fishing down the marine food web” hypothesis, other indicators did show the continued scarcity of major high trophic level categories and fisheries target species. Overall, the results indicate that the analysis of fishery landings, or of certain other indicators alone, can mask real changes. Rather, a joint ecological-econometric analysis provides better evidence of the direction of ecosystem pressures and stock health. This method for detecting market changes across the food web may be particularly helpful for systems considered data-poor but where fish market data have been archived. This study further elucidates historical changes and fishing impacts in the South Brazil Bight ecosystem.

  8. DEEPWATER AND NEARSHORE FOOD WEB CHARACTERIZATIONS IN LAKE SUPERIOR

    EPA Science Inventory

    Due to the difficulty associated with sampling deep aquatic systems, food web relationships among deepwater fauna are often poorly known. We are characterizing nearshore versus offshore habitats in the Great Lakes and investigating food web linkages among profundal, pelagic, and ...

  9. Extinction risk and structure of a food web model

    NASA Astrophysics Data System (ADS)

    Pękalski, Andrzej; Szwabiński, Janusz; Bena, Ioana; Droz, Michel

    2008-03-01

    We investigate in detail the model of a trophic web proposed by Amaral and Meyer [Phys. Rev. Lett. 82, 652 (1999)]. We focus on small-size systems that are relevant for real biological food webs and for which the fluctuations play an important role. We show, using Monte Carlo simulations, that such webs can be nonviable, leading to extinction of all species in small and/or weakly coupled systems. Estimations of the extinction times and survival chances are also given. We show that before the extinction the fraction of highly connected species (“omnivores”) is increasing. Viable food webs exhibit a pyramidal structure, where the density of occupied niches is higher at lower trophic levels, and moreover the occupations of adjacent levels are closely correlated. We also demonstrate that the distribution of the lengths of food chains has an exponential character and changes weakly with the parameters of the model. On the contrary, the distribution of avalanche sizes of the extinct species depends strongly on the connectedness of the web. For rather loosely connected systems, we recover the power-law type of behavior with the same exponent as found in earlier studies, while for densely connected webs the distribution is not of a power-law type.

  10. Functional changes due to invasive species: Food web shifts at shallow Posidonia oceanica seagrass beds colonized by the alien macroalga Caulerpa racemosa

    NASA Astrophysics Data System (ADS)

    Deudero, S.; Box, A.; Alós, J.; Arroyo, N. L.; Marbà, N.

    2011-06-01

    Multiple stable isotope analyses were used to examine the trophic shifts at faunal assemblages within the invading macroalga Caulerpa racemosa in comparison to established communities of Posidonia oceanica seagrass meadows. Sampling of macrobenthic invertebrates and their potential food sources of algal mats and seagrass meadows in Mallorca (NW Mediterranean) showed differences in species composition of faunal and primary producers among seagrass and C. racemosa. Accordingly, changes in food web structure and trophic guilds were observed, not only at species level but also at community level. The carbon and nitrogen isotope signatures of herbivores, detritivores and deposit feeders confirmed that the seagrass provided a small contribution to the macrofaunal organisms. δ 13C at the P. oceanica seagrass and at the C. racemosa assemblages differed, ranging from -6.19 to -21.20‰ and -2.67 to -31.41‰, respectively. δ 15N at the Caulerpa mats was lower (ranging from 2.64 to 10.45‰) than that at the seagrass meadows (3.51-12. 94‰). Significant differences in isotopic signatures and trophic level among trophic guilds at P. oceanica and C. racemosa were found. N fractionation at trophic guild level considerable differed between seagrass and macroalgae mats, especially for detritivores, deposit feeders, and herbivores. Filter feeders slightly differed with a relatively lower N signal at the seagrass and CR values at community level and at trophic guild level were higher in the C. racemosa invaded habitats indicating an increase in diversity of basal resource pools. C. racemosa did seem to broaden the niche diversity of the P. oceanica meadows it colonised at the base of the food web, may be due to the establishment of a new basal resource. The extent of the effects of invasive species on ecosystem functioning is a fundamental issue in conservation ecology. The observed changes in invertebrate and macrophytic composition, stable isotope signatures of concomitant

  11. Land use alters the resistance and resilience of soil food webs to drought

    USGS Publications Warehouse

    de Vries, Franciska T.; Liiri, Mira E.; Bjørnlund, Lisa; Bowker, Matthew A.; Christensen, Søren; Setälä, Heikki; Bardgett, Richard D.

    2012-01-01

    Soils deliver several ecosystem services including carbon sequestration and nutrient cycling, which are of central importance to climate mitigation and sustainable food production. Soil biota play an important role in carbon and nitrogen cycling, and, although the effects of land use on soil food webs are well documented the consequences for their resistance and resilience to climate change are not known. We compared the resistance and resilience to drought--which is predicted to increase under climate change of soil food webs of two common land-use systems: intensively managed wheat with a bacterial-based soil food web and extensively managed grassland with a fungal-based soil food web. We found that the fungal-based food web, and the processes of C and N loss it governs, of grassland soil was more resistant, although not resilient, and better able to adapt to drought than the bacterial-based food web of wheat soil. Structural equation modelling revealed that fungal-based soil food webs and greater microbial evenness mitigated C and N loss. Our findings show that land use strongly affects the resistance and resilience of soil food webs to climate change, and that extensively managed grassland promotes more resistant, and adaptable, fungal-based soil food webs.

  12. Infectious disease agents mediate interaction in food webs and ecosystems

    PubMed Central

    Selakovic, Sanja; de Ruiter, Peter C.; Heesterbeek, Hans

    2014-01-01

    Infectious agents are part of food webs and ecosystems via the relationship with their host species that, in turn, interact with both hosts and non-hosts. Through these interactions, infectious agents influence food webs in terms of structure, functioning and stability. The present literature shows a broad range of impacts of infectious agents on food webs, and by cataloguing that range, we worked towards defining the various mechanisms and their specific effects. To explore the impact, a direct approach is to study changes in food-web properties with infectious agents as separate species in the web, acting as additional nodes, with links to their host species. An indirect approach concentrates not on adding new nodes and links, but on the ways that infectious agents affect the existing links across host and non-host nodes, by influencing the ‘quality’ of consumer–resource interaction as it depends on the epidemiological state host involved. Both approaches are natural from an ecological point of view, but the indirect approach may connect more straightforwardly to commonly used tools in infectious disease dynamics. PMID:24403336

  13. Press perturbations and indirect effects in real food webs.

    PubMed

    Montoya, José M; Woodward, Guy; Emmerson, Mark C; Solé, Ricard V

    2009-09-01

    The prediction of the effects of disturbances in natural systems is limited by the general lack of knowledge on the strength of species interactions, i.e., the effect of one species on the population growth rate of another, and by the uncertainty of the effects that may be manifested via indirect pathways within the food web. Here we explored the consequences of changes in species populations for the remaining species within nine exceptionally well-characterized empirical food webs, for which, unlike the vast majority of other published webs, feeding links have been fully quantified. Using the inverse of the Jacobian matrix, we found that perturbations to species with few connections have larger net effects (considering both direct and indirect pathways between two species) on the rest of the food web than do disturbances to species that are highly connected. For 40% of predator-prey links, predators had positive net effects on prey populations, due to the predominance of indirect interactions. Our results highlight the fundamental, but often counterintuitive, role of indirect effects for the maintenance of food web complexity and biodiversity.

  14. A Biomass Flow Approach to Population Models and Food Webs

    PubMed Central

    Getz, Wayne M.

    2011-01-01

    The dominant differential equation paradigm for modeling the population dynamics of species interacting in the framework of a food web retains at its core the basic prey-predator and competition models formulation by Alfred J. Lotka (1880–1945) and Vito Volterra (1860–1940) nearly nine decades ago. This paradigm lacks a trophic-level-independent formulation of population growth leading to ambiguities in how to treat populations that are simultaneously both prey and predator. Also, this paradigm does not fundamentally include inertial (i.e. change resisting) processes needed to account for the response of populations to fluctuating resource environments. Here I present an approach that corrects both these deficits and provides a unified framework for accounting for biomass transformation in food webs that include both live and dead components of all species in the system. This biomass transformation formulation (BTW) allows for a unified treatment of webs that include consumers of both live and dead material—both carnivores and carcasivores, herbivores and detritivores—and incorporates scavengers, parasites, and other neglected food web consumption categories in a coherent manner. I trace how BTW is an outgrowth of the metaphysiological growth modeling paradigm and I provide a general compact formulation of BTW in terms of a three-variable differential equation formulation for each species in the food web: viz. live biomass, dead biomass, and a food-intake-related measure called deficit-stress. I then illustrate the application of this new paradigm to provide insights into two-species competition in variable environments and discuss application of BTW to food webs that incorporate parasites and pathogens. PMID:27688596

  15. A Biomass Flow Approach to Population Models and Food Webs.

    PubMed

    Getz, Wayne M

    2012-02-01

    The dominant differential equation paradigm for modeling the population dynamics of species interacting in the framework of a food web retains at its core the basic prey-predator and competition models formulation by Alfred J. Lotka (1880-1945) and Vito Volterra (1860-1940) nearly nine decades ago. This paradigm lacks a trophic-level-independent formulation of population growth leading to ambiguities in how to treat populations that are simultaneously both prey and predator. Also, this paradigm does not fundamentally include inertial (i.e. change resisting) processes needed to account for the response of populations to fluctuating resource environments. Here I present an approach that corrects both these deficits and provides a unified framework for accounting for biomass transformation in food webs that include both live and dead components of all species in the system. This biomass transformation formulation (BTW) allows for a unified treatment of webs that include consumers of both live and dead material-both carnivores and carcasivores, herbivores and detritivores-and incorporates scavengers, parasites, and other neglected food web consumption categories in a coherent manner. I trace how BTW is an outgrowth of the metaphysiological growth modeling paradigm and I provide a general compact formulation of BTW in terms of a three-variable differential equation formulation for each species in the food web: viz. live biomass, dead biomass, and a food-intake-related measure called deficit-stress. I then illustrate the application of this new paradigm to provide insights into two-species competition in variable environments and discuss application of BTW to food webs that incorporate parasites and pathogens.

  16. Mycoloop: chytrids in aquatic food webs.

    PubMed

    Kagami, Maiko; Miki, Takeshi; Takimoto, Gaku

    2014-01-01

    Parasites are ecologically significant in various ecosystems through their role in shaping food web structure, facilitating energy transfer, and controlling disease. Here in this review, we mainly focus on parasitic chytrids, the dominant parasites in aquatic ecosystems, and explain their roles in aquatic food webs, particularly as prey for zooplankton. Chytrids have a free-living zoosporic stage, during which they actively search for new hosts. Zoospores are excellent food for zooplankton in terms of size, shape, and nutritional quality. In the field, densities of chytrids can be high, ranging from 10(1) to 10(9) spores L(-1). When large inedible phytoplankton species are infected by chytrids, nutrients within host cells are transferred to zooplankton via the zoospores of parasitic chytrids. This new pathway, the "mycoloop," may play an important role in shaping aquatic ecosystems, by altering sinking fluxes or determining system stability. The grazing of zoospores by zooplankton may also suppress outbreaks of parasitic chytrids. A food web model demonstrated that the contribution of the mycoloop to zooplankton production increased with nutrient availability and was also dependent on the stability of the system. Further studies with advanced molecular tools are likely to discover greater chytrid diversity and evidence of additional mycoloops in lakes and oceans.

  17. Effects of extinction on food web structures on an evolutionary time scale.

    PubMed

    Hironaga, Ryo; Yamamura, Norio

    2010-03-21

    Extinction affected food web structure in paleoecosystems. Recent theoretical studies that examined the effects of extinction intensity on food web structure on ecological time scales have considered extinction to involve episodic events, with pre-extinction food webs becoming established without dynamics. However, in terms of the paleontological time scale, food web structures are generated from feedback with repeated extinctions, because extinction frequency is affected by food web structure, and food web structure itself is a product of previous extinctions. We constructed a simulation model of changes in tri-trophic-level food webs to examine how continual extinction events affect food webs on an evolutionary time scale. We showed that under high extinction intensity (1) species diversity, especially that of consumer species, decreased; (2) the total population density at each trophic level decreased, while the densities of individual species increased; and (3) the trophic link density of the food web increased. In contrast to previous models, our results were based on an assumption of long-term food web development and are able to explain overall trends posited by empirical investigations based on fossil records.

  18. Quantitative approaches to the analysis of stable isotope food web data.

    PubMed

    Schmidt, Stephanie N; Olden, Julian D; Solomon, Christopher T; Vander Zanden, M Jake

    2007-11-01

    Ecologists use stable isotopes (delta13C, delta15N) to better understand food webs and explore trophic interactions in ecosystems. Traditionally, delta13C vs. delta15N bi-plots have been used to describe food web structure for a single time period or ecosystem. Comparisons of food webs across time and space are increasing, but development of statistical approaches for testing hypotheses regarding food web change has lagged behind. Here we present statistical methodologies for quantitatively comparing stable isotope food web data. We demonstrate the utility of circular statistics and hypothesis tests for quantifying directional food web differences using two case studies: an arthropod salt marsh community across a habitat gradient and a freshwater fish community from Lake Tahoe, USA, over a 120-year time period. We calculated magnitude and mean angle of change (theta) for each species in food web space using mean delta13C and delta15N of each species as the x, y coordinates. In the coastal salt marsh, arthropod consumers exhibited a significant shift toward dependence on Spartina, progressing from a habitat invaded by Phragmites to a restored Spartina habitat. In Lake Tahoe, we found that all species from the freshwater fish community shifted in the same direction in food web space toward more pelagic-based production with the introduction of nonnative Mysis relicta and onset of cultural eutrophication. Using circular statistics to quantitatively analyze stable isotope food web data, we were able to gain significant insight into patterns and changes in food web structure that were not evident from qualitative comparisons. As more ecologists incorporate a food web perspective into ecosystem analysis, these statistical tools can provide a basis for quantifying directional food web differences from standard isotope data.

  19. Trophic coherence determines food-web stability

    PubMed Central

    Johnson, Samuel; Domínguez-García, Virginia; Donetti, Luca; Muñoz, Miguel A.

    2014-01-01

    Why are large, complex ecosystems stable? Both theory and simulations of current models predict the onset of instability with growing size and complexity, so for decades it has been conjectured that ecosystems must have some unidentified structural property exempting them from this outcome. We show that trophic coherence—a hitherto ignored feature of food webs that current structural models fail to reproduce—is a better statistical predictor of linear stability than size or complexity. Furthermore, we prove that a maximally coherent network with constant interaction strengths will always be linearly stable. We also propose a simple model that, by correctly capturing the trophic coherence of food webs, accurately reproduces their stability and other basic structural features. Most remarkably, our model shows that stability can increase with size and complexity. This suggests a key to May’s paradox, and a range of opportunities and concerns for biodiversity conservation. PMID:25468963

  20. Trophic coherence determines food-web stability.

    PubMed

    Johnson, Samuel; Domínguez-García, Virginia; Donetti, Luca; Muñoz, Miguel A

    2014-12-16

    Why are large, complex ecosystems stable? Both theory and simulations of current models predict the onset of instability with growing size and complexity, so for decades it has been conjectured that ecosystems must have some unidentified structural property exempting them from this outcome. We show that trophic coherence--a hitherto ignored feature of food webs that current structural models fail to reproduce--is a better statistical predictor of linear stability than size or complexity. Furthermore, we prove that a maximally coherent network with constant interaction strengths will always be linearly stable. We also propose a simple model that, by correctly capturing the trophic coherence of food webs, accurately reproduces their stability and other basic structural features. Most remarkably, our model shows that stability can increase with size and complexity. This suggests a key to May's paradox, and a range of opportunities and concerns for biodiversity conservation.

  1. Changes in food web structure under scenarios of overfishing in the southern Benguela: Comparison of the Ecosim and OSMOSE modelling approaches

    NASA Astrophysics Data System (ADS)

    Travers, M.; Watermeyer, K.; Shannon, L. J.; Shin, Y.-J.

    2010-01-01

    Ecosystem models provide a platform allowing exploration into the possible responses of marine food webs to fishing pressure and various potential management decisions. In this study we investigate the particular effects of overfishing on the structure and function of the southern Benguela food web, using two models with different underlying assumptions: the spatialized, size-based individual-based model, OSMOSE, and the trophic mass-balance model, Ecopath with Ecosim (EwE). Starting from the same reference state of the southern Benguela upwelling ecosystem during the 1990s, we compare the response of the food web to scenarios of overfishing using these two modelling approaches. A scenario of increased fishing mortality is applied to two distinct functional groups: i) two species of Cape hake, representing important target predatory fish, and ii) the forage species anchovy, sardine and redeye. In these simulations, fishing mortality on the selected functional groups is doubled for 10 years, followed by 10 years at the initial fishing mortality. We compare the food web states before the increase of fishing mortality, after 10 years of overfishing and after a further 10 years during which fishing was returned to initial levels. In order to compare the simulated food web structures with the reference state, and between the two modelling approaches, we use a set of trophic indicators: the mean trophic level of the community and in catches, the trophic pyramid (biomass per discrete trophic level), and the predatory/forage fish biomass ratio. OSMOSE and EwE present globally similar results for the trophic functioning of the ecosystem under fishing pressure: the biomass of targeted species decreases whereas that of their potential competitors increases. The reaction of distant species is more diverse, depending on the feeding links between the compartments. The mean trophic level of the community does not vary enough to be used for assessing ecosystem impacts of fishing

  2. Global synthesis suggests that food web connectance correlates to invasion resistance.

    PubMed

    Smith-Ramesh, Lauren M; Moore, Alexandria C; Schmitz, Oswald J

    2017-02-01

    Biological invasions are a key component of global change, and understanding the drivers of global invasion patterns will aid in assessing and mitigating the impact of invasive species. While invasive species are most often studied in the context of one or two trophic levels, in reality species invade communities comprised of complex food webs. The complexity and integrity of the native food web may be a more important determinant of invasion success than the strength of interactions between a small subset of species within a larger food web. Previous efforts to understand the relationship between food web properties and species invasions have been primarily theoretical and have yielded mixed results. Here, we present a synthesis of empirical information on food web connectance and species invasion success gathered from different sources (estimates of food web connectance from the primary literature and estimates of invasion success from the Global Invasive Species Database as well as the primary literature). Our results suggest that higher-connectance food webs tend to host fewer invaders and exert stronger biotic resistance compared to low-connectance webs. We argue that while these correlations cannot be used to infer a causal link between food web connectance and habitat invasibility, the promising findings beg for further empirical research that deliberately tests for relationships between food web connectance and invasion.

  3. Parasites in food webs: the ultimate missing links.

    PubMed

    Lafferty, Kevin D; Allesina, Stefano; Arim, Matias; Briggs, Cherie J; De Leo, Giulio; Dobson, Andrew P; Dunne, Jennifer A; Johnson, Pieter T J; Kuris, Armand M; Marcogliese, David J; Martinez, Neo D; Memmott, Jane; Marquet, Pablo A; McLaughlin, John P; Mordecai, Erin A; Pascual, Mercedes; Poulin, Robert; Thieltges, David W

    2008-06-01

    Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists.

  4. Parasites in food webs: the ultimate missing links

    PubMed Central

    Lafferty, Kevin D; Allesina, Stefano; Arim, Matias; Briggs, Cherie J; De Leo, Giulio; Dobson, Andrew P; Dunne, Jennifer A; Johnson, Pieter T J; Kuris, Armand M; Marcogliese, David J; Martinez, Neo D; Memmott, Jane; Marquet, Pablo A; McLaughlin, John P; Mordecai, Erin A; Pascual, Mercedes; Poulin, Robert; Thieltges, David W

    2008-01-01

    Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists. PMID:18462196

  5. Parasites in food webs: the ultimate missing links

    USGS Publications Warehouse

    Lafferty, Kevin D.; Allesina, Stefano; Arim, Matias; Briggs, Cherie J.; De Leo, Giulio A.; Dobson, Andrew P.; Dunne, Jennifer A.; Johnson, Pieter T.J.; Kuris, Armand M.; Marcogliese, David J.; Martinez, Neo D.; Memmott, Jane; Marquet, Pablo A.; McLaughlin, John P.; Mordecai, Eerin A.; Pascual, Mercedes; Poulin, Robert; Thieltges, David W.

    2008-01-01

    Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists.

  6. Evidence for the persistence of food web structure after amphibian extirpation in a Neotropical stream.

    PubMed

    Barnum, Thomas R; Drake, John M; Colón-Gaud, Checo; Rugenski, Amanda T; Frauendorf, Therese C; Connelly, Scott; Kilham, Susan S; Whiles, Matt R; Lips, Karen R; Pringle, Catherine M

    2015-08-01

    Species losses are predicted to simplify food web structure, and disease-driven amphibian declines in Central America offer an opportunity to test this prediction. Assessment of insect community composition, combined with gut content analyses, was used to generate periphyton-insect food webs for a Panamanian stream, both pre- and post-amphibian decline. We then used network analysis to assess the effects of amphibian declines on food web structure. Although 48% of consumer taxa, including many insect taxa, were lost between pre- and post-amphibian decline sampling dates, connectance declined by less than 3%. We then quantified the resilience of food web structure by calculating the number of expected cascading extirpations from the loss of tadpoles. This analysis showed the expected effects of species loss on connectance and linkage density to be more than 60% and 40%, respectively, than were actually observed. Instead, new trophic linkages in the post-decline food web reorganized the food web topology, changing the identity of "hub" taxa, and consequently reducing the effects of amphibian declines on many food web attributes. Resilience of food web attributes was driven by a combination of changes in consumer diets, particularly those of insect predators, as well as the appearance of generalist insect consumers, suggesting that food web structure is maintained by factors independent of the original trophic linkages.

  7. Managing Change on the Web.

    ERIC Educational Resources Information Center

    Francisco-Revilla, Luis; Shipman, Frank; Furuta, Richard; Karadkar, Unmil; Arora, Avital

    Increasingly, digital libraries are being defined as collection pointers to World Wide Web-based resources rather than collections that hold the resources themselves. Maintaining these collections is challenging due to distributed document ownership and high fluidity. Typically a collection's maintainer has to assess the relevance of changes with…

  8. Critical patch sizes for food-web modules.

    PubMed

    Martinson, Holly M; Fagan, William F; Denno, Robert F

    2012-08-01

    Because patch size and connectivity may strongly impact the assemblage of species that occur on a patch, the types of food-web interactions that occur among those species may also depend on spatial structure. Here, we identify whether food-web interactions among salt-marsh-inhabiting arthropods vary with patch size and connectivity, and how such changes in trophic structure might feed back to influence the spatial distribution of prey. In a multiyear survey, patch-restricted predators exhibited steeper occupancy-patch-size relationships than herbivores, and species' critical patch sizes were correlated with overall rarity. As a result, the presence of food-web modules depended strongly on patch size: large and well-connected patches supported complex food-web modules, but only the simplest modules involving the most abundant species were found on small patches. Habitat-generalist spiders dominated on small patches, and predation pressure from such species may contribute to the observed lower densities of mesopredators on small patches. Overall, patch size and connectivity influenced the types of modules present on a patch through differential loss of rare, patch-restricted predators, but predation by generalist predators may be a key mechanism influencing the spatial structure of certain prey species.

  9. The trophodynamics of PCBs in the Lake Ontario food web

    SciTech Connect

    Metcalfe, T.L.; Metcalfe, C.D.

    1995-12-31

    Samples of water, sediment, invertebrates, fish, and herring gull eggs were collected in north-central Lake Ontario and were analyzed to determine the concentrations of PCBs, including non-ortho substituted PCB congeners, in the benthic and pelagic components of the Lake Ontario food web. There was biomagnification of PCBs in the food web from benthic and planktonic invertebrates through to lake trout and gulls. However, all of the fish species had about the same lipid-normalized concentrations of PCBs. The relative proportions of the PCB congeners changed as they passed through the food web. An index of metabolism for each PCB congener was calculated by comparing the concentrations of PCB congeners in various predator/prey groupings within the food web. These data indicate that invertebrates, fish and gulls have different capabilities in metabolizing and eliminating specific PCB congeners. While tri and tetrachlorinated congeners with no chlorine substitution at meta-para carbons on the biphenyl ring were readily metabolized by all taxa, only gulls appeared to be capable of metabolizing the PCBs with no chlorine substitution at ortho-meta positions. The trophodynamics of nonortho substituted (coplanar) PCBs did not differ from other PCB congeners of similar chlorine number, which indicates that non-ortho congeners are not any more persistent in biota than other PCBs.

  10. Material exchange and food web of seagrass beds in the Sylt-Rømø Bight: how significant are community changes at the ecosystem level?

    NASA Astrophysics Data System (ADS)

    Asmus, H.; Asmus, R.

    2000-07-01

    subtidal part, the function of the ecosystem as a source for particles increased, supposing that all seagrass beds were lost from the area. During the vegetation period, seagrass beds act as a storage compartment for material accumulated in the living biomass of the community. There was great biodiversity among the plant and animal groups found in intertidal seagrass beds of the Sylt-Rømø Bay, representing 50-86% of the total number of species investigated, depending on the particular group. Since most species are not exclusively seagrass residents, the loss of intertidal seagrass beds would be of minor importance for biodiversity at the ecosystem level. Food web structure in seagrass beds is different from other intertidal communities. Primary production and detritus input is high, but secondary production is similar to that of unvegetated areas, although the relative importance of the trophic guilds is different. The loss of seagrass beds leads to profound alterations in the food web of the total ecosystem. Historical as well as recent changes in material fluxes and energy flow due to man-made alterations to the ecosystem are discussed.

  11. Computer simulations of sympatric speciation in a simple food web

    NASA Astrophysics Data System (ADS)

    Luz-Burgoa, K.; Dell, Tony; de Oliveira, S. Moss

    2005-07-01

    Galapagos finches, have motivated much theoretical research aimed at understanding the processes associated with the formation of the species. Inspired by them, in this paper we investigate the process of sympatric speciation in a simple food web model. For that we modify the individual-based Penna model that has been widely used to study aging as well as other evolutionary processes. Initially, our web consists of a primary food source and a single herbivore species that feeds on this resource. Subsequently we introduce a predator that feeds on the herbivore. In both instances we manipulate directly a basal resource distribution and monitor the changes in the populations. Sympatric speciation is obtained for the top species in both cases, and our results suggest that the speciation velocity depends on how far up, in the food chain, the focus population is feeding. Simulations are done with three different sexual imprintinglike mechanisms, in order to discuss adaptation by natural selection.

  12. Food web model with detritus path

    NASA Astrophysics Data System (ADS)

    Szwabiński, Janusz; Pękalski, Andrzej; Bena, Ioana; Droz, Michel

    2010-07-01

    We present and study a lattice (Monte Carlo) model of a food web consisting of three levels. Agents on the lowest level produce food from dead agents (detritus) of the upper levels and are themselves eaten by the first level species, which in turn are prey for the top level species. Agents which do not find food in a given time, die with a given probability, while eating enables them to produce offspring in their neighborhood. This rule applies to species on all levels, including the lowest one. The dynamics is therefore nutrient limited. We are considering two pathways - grazers and detritus (using dead organic matter). We show that the emerging dynamics is more complex than the ordinary predator-prey systems in which bottom species are indestructible. We investigate the viability of our model and we construct appropriate (extinct-alive) phase diagrams. We demonstrate how the temporal fluctuations in the densities of the three populations are correlated. We show also that the density of the middle level agents plays the key role in the viability of the investigated food web.

  13. Exploring Fish Diversity as a Determinant of Ecosystem Properties in Aquatic Food Webs

    ERIC Educational Resources Information Center

    Carey, Michael P.

    2009-01-01

    Dramatic biodiversity changes occurring globally from species loss and invasion have altered native food webs and ecosystem processes. My research objectives are to understand the consequences of fish diversity to freshwater systems by (1) examining the food web consequences of multiple top predators, (2) determining how biodiversity influences…

  14. Food web heterogeneity and succession in created saltmarshes

    USGS Publications Warehouse

    Nordstrom, M C; Demopoulos, Amanda; Whitcraft, CR; Rismondo, A.; McMillan, P.; Gonzales, J P; Levin, L A

    2015-01-01

    1. Ecological restoration must achieve functional as well as structural recovery. Functional metrics for reestablishment of trophic interactions can be used to complement traditional monitoring of structural attributes. In addition, topographic effects on food web structure provide added information within a restoration context; often, created sites may require spatial heterogeneity to effectively match structure and function of natural habitats. 2. We addressed both of these issues in our study of successional development of benthic food web structure, with focus on bottom–up driven changes in macroinvertebrate consumer assemblages in the salt marshes of the Venice Lagoon, Italy. We combined quantified estimates of the changing community composition with stable isotope data (13C:12C and 15N:14N) to compare the general trophic structure between created (2–14 years) marshes and reference sites and along topographic elevation gradients within salt marshes. 3. Macrofaunal invertebrate consumers exhibited local, habitat-specific trophic patterns. Stable isotope-based trophic structure changed with increasing marsh age, in particular with regards to mid-elevation (Salicornia) habitats. In young marshes, the mid-elevation consumer signatures resembled those of unvegetated ponds. The mid elevation of older and natural marshes had a more distinct Salicornia-zone food web, occasionally resembling that of the highest (Sarcocornia-dominated) elevation. In summary, this indicates that primary producers and availability of vascular plant detritus structure consumer trophic interactions and the flow of carbon. 4. Functionally different consumers, subsurface-feeding detritivores (Oligochaeta) and surface grazers (Hydrobia sp.), showed distinct but converging trajectories of isotopic change over time, indicating that successional development may be asymmetric between ‘brown’ (detrital) guilds and ‘green’ (grazing) guilds in the food web. 5. Synthesis and applications

  15. Interannual variability in the Northern California Current food web structure: Changes in energy flow pathways and the role of forage fish, euphausiids, and jellyfish

    NASA Astrophysics Data System (ADS)

    Ruzicka, James J.; Brodeur, Richard D.; Emmett, Robert L.; Steele, John H.; Zamon, Jeannette E.; Morgan, Cheryl A.; Thomas, Andrew C.; Wainwright, Thomas C.

    2012-09-01

    The Northern California Current (NCC) is a seasonally productive and open ecosystem. It is home to both a diverse endemic community and to seasonally transient species. Productivity and food web structure vary seasonally, interannually, and decadally due to variability in coastal upwelling, climate-scale physical processes, and the migratory species entering the system. The composition of the pelagic community varies between years, including changes to mid-trophic level groups that represent alternate energy-transfer pathways between lower and upper trophic levels (forage fishes, euphausiids, jellyfish). Multiple data sets, including annual spring and summer mesoscale surveys of the zooplankton, pelagic fish, and seabird communities, were used to infer NCC trophic network arrangements and develop end-to-end models for each of the 2003-2007 upwelling seasons. Each model was used to quantify the interannual variability in energy-transfer efficiency from bottom to top trophic levels. When each model was driven under an identical nutrient input rate, substantial differences in the energy available to each functional group were evident. Scenario analyses were used to examine the roles of forage fishes, euphausiids, and jellyfish (small gelatinous zooplankton and large carnivorous jellyfish) as alternate energy transfer pathways. Euphausiids were the more important energy transfer pathway; a large proportion of the lower trophic production consumed was transferred to higher trophic levels. In contrast, jellyfish acted as a production loss pathway; little of the production consumed was passed upwards. Analysis of the range of ecosystem states observed interannually and understanding system sensitivity to variability among key trophic groups improves our ability to predict NCC ecosystem response to short- and long-term environmental change.

  16. Native and nonnative fish populations of the Colorado River are food limited--evidence from new food web analyses

    USGS Publications Warehouse

    Kennedy, Theodore A.; Cross, Wyatt F.; Hall, Robert O.; Baxter, Colden V.; Rosi-Marshall, Emma J.

    2013-01-01

    Fish populations in the Colorado River downstream from Glen Canyon Dam appear to be limited by the availability of high-quality invertebrate prey. Midge and blackfly production is low and nonnative rainbow trout in Glen Canyon and native fishes in Grand Canyon consume virtually all of the midge and blackfly biomass that is produced annually. In Glen Canyon, the invertebrate assemblage is dominated by nonnative New Zealand mudsnails, the food web has a simple structure, and transfers of energy from the base of the web (algae) to the top of the web (rainbow trout) are inefficient. The food webs in Grand Canyon are more complex relative to Glen Canyon, because, on average, each species in the web is involved in more interactions and feeding connections. Based on theory and on studies from other ecosystems, the structure and organization of Grand Canyon food webs should make them more stable and less susceptible to large changes following perturbations of the flow regime relative to food webs in Glen Canyon. In support of this hypothesis, Grand Canyon food webs were much less affected by a 2008 controlled flood relative to the food web in Glen Canyon.

  17. Spatial complexity enhances predictability in food webs

    PubMed Central

    Mougi, Akihiko

    2017-01-01

    The prediction of an ecosystem’s response to an environmental disturbance or the artificial control of ecosystems is a challenging task in ecology. Ecological theory predicts that disturbances frequently result in unexpected responses between interacting species due to the many indirect interactions within a complex community. However, such indeterminacy appears to be unusual in nature. Here using a meta-community food web, I show that spatiality is key to resolving this disparity. A moderate level of spatial coupling strength between habitats due to species migration increases the possibility of expected responses to press perturbation or predictability. Moreover, predictability increases with increasing spatial complexity, as measured by the number of local food webs and their connectivity. A meta-community network can attenuate the propagation of disturbances through indirect pathways due to species emigration to other habitats, thereby preserving the expected effect on the interacting species. These results suggest that the isolation of communities due to habitat destruction decreases the predictability of communities, thereby complicating the control of ecosystems. PMID:28240306

  18. Community fluctuations and local extinction in a planktonic food web.

    PubMed

    Segura, A M; Calliari, D; Lan, B L; Fort, H; Widdicombe, C E; Harmer, R; Arim, M

    2017-04-01

    Determining statistical patterns irrespective of interacting agents (i.e. macroecology) is useful to explore the mechanisms driving population fluctuations and extinctions in natural food webs. Here, we tested four predictions of a neutral model on the distribution of community fluctuations (CF) and the distributions of persistence times (APT). Novel predictions for the food web were generated by combining (1) body size-density scaling, (2) Taylor's law and (3) low efficiency of trophic transference. Predictions were evaluated on an exceptional data set of plankton with 15 years of weekly samples encompassing c. 250 planktonic species from three trophic levels, sampled in the western English Channel. Highly symmetric non-Gaussian distributions of CF support zero-sum dynamics. Variability in CF decreased while a change from an exponential to a power law distribution of APT from basal to upper trophic positions was detected. Results suggest a predictable but profound effect of trophic position on fluctuations and extinction in natural communities.

  19. Benchmarking successional progress in a quantitative food web.

    PubMed

    Boit, Alice; Gaedke, Ursula

    2014-01-01

    Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of

  20. Benchmarking Successional Progress in a Quantitative Food Web

    PubMed Central

    Boit, Alice; Gaedke, Ursula

    2014-01-01

    Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of

  1. Metacommunity theory explains the emergence of food web complexity.

    PubMed

    Pillai, Pradeep; Gonzalez, Andrew; Loreau, Michel

    2011-11-29

    Food webs are highly complex ecological networks, dynamic in both space and time. Metacommunity models are now at the core of unified theories of biodiversity, but to date they have not addressed food web complexity. Here we show that metacommunity theory can explain the emergence of species-rich food webs with complex network topologies. Our analysis shows that network branching in the food web is maximized at intermediate colonization rates and limited dispersal scales, which also leads to concomitant peaks in species diversity. Increased food web complexity and species diversity are made possible by the structural role played by network branches that are supported by omnivore and generalist feeding links. Thus, in contrast to traditional food web theory, which emphasizes the destabilizing effect of omnivory feeding in closed systems, metacommunity theory predicts that these feeding links, which are commonly observed in empirical food webs, play a critical structural role as food webs assemble in space. As this mechanism functions at the metacommunity level, evidence for its operation in nature will be obtained through multiscale surveys of food web structure. Finally, we apply our theory to reveal the effects of habitat destruction on network complexity and metacommunity diversity.

  2. Trophic positioning of meiofauna revealed by stable isotopes and food web analyses.

    PubMed

    Schmid-Araya, Jenny M; Schmid, Peter E; Tod, Steven P; Esteban, Genoveva F

    2016-11-01

    Despite important advances in the ecology of river food webs, the strength and nature of the connection between the meio- and macrofaunal components of the web are still debated. Some unresolved issues are the effects of the inclusion of meiofaunal links and their temporal variations on the overall river food web properties, and the significance of autochthonous and allochthonous material for these components. In the present study, we conducted analyses of gut content of macro- and meiofauna and stable isotope analyses of meiofauna to examine seasonal food webs of a chalk stream. The results of the gut content analyses, confirmed by the δ(13) C signatures, revealed a seasonal shift from a dependence on autochthonous (biofilm) to allochthonous food sources. Here, we demonstrate that aggregating basal or meiofaunal species into single categories affects key web properties such as web size, links, linkage density, and predator-prey ratios. More importantly, seasonal variation in attributes characterized the entire web and these changes persist regardless of taxonomic resolution. Furthermore, our analyses evidenced discrete variations in δ(15) N across the meiofauna community with a trophic structure that confirms gut content analyses, placing the meiofauna high in the food web. We, therefore, conclude that small-body-sized taxa can occur high in dynamic river food webs, questioning assumptions that trophic position increases with body size and that webs are static.

  3. Anthropogenic effects are associated with a lower persistence of marine food webs

    PubMed Central

    Gilarranz, Luis J.; Mora, Camilo; Bascompte, Jordi

    2016-01-01

    Marine coastal ecosystems are among the most exposed to global environmental change, with reported effects on species biomass, species richness and length of trophic chains. By combining a biologically informed food-web model with information on anthropogenic influences in 701 sites across the Caribbean region, we show that fishing effort, human density and thermal stress anomaly are associated with a decrease in local food-web persistence. The conservation status of the site, in turn, is associated with an increase in food-web persistence. Some of these associations are explained through effects on food-web structure and total community biomass. Our results unveil a hidden footprint of human activities. Even when food webs may seem healthy in terms of the presence and abundance of their constituent species, they may be losing the capacity to withstand further environmental degradation. PMID:26867790

  4. Developing a broader scientific foundation for river restoration: Columbia River food webs.

    PubMed

    Naiman, Robert J; Alldredge, J Richard; Beauchamp, David A; Bisson, Peter A; Congleton, James; Henny, Charles J; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N; Pearcy, William G; Rieman, Bruce E; Ruggerone, Gregory T; Scarnecchia, Dennis; Smouse, Peter E; Wood, Chris C

    2012-12-26

    Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure--without explicitly considering food webs--has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

  5. Rescaling the trophic structure of marine food webs.

    PubMed

    Hussey, Nigel E; Macneil, M Aaron; McMeans, Bailey C; Olin, Jill A; Dudley, Sheldon F J; Cliff, Geremy; Wintner, Sabine P; Fennessy, Sean T; Fisk, Aaron T

    2014-02-01

    Measures of trophic position (TP) are critical for understanding food web interactions and human-mediated ecosystem disturbance. Nitrogen stable isotopes (δ(15) N) provide a powerful tool to estimate TP but are limited by a pragmatic assumption that isotope discrimination is constant (change in δ(15) N between predator and prey, Δ(15) N = 3.4‰), resulting in an additive framework that omits known Δ(15) N variation. Through meta-analysis, we determine narrowing discrimination from an empirical linear relationship between experimental Δ(15) N and δ(15) N values of prey consumed. The resulting scaled Δ(15) N framework estimated reliable TPs of zooplanktivores to tertiary piscivores congruent with known feeding relationships that radically alters the conventional structure of marine food webs. Apex predator TP estimates were markedly higher than currently assumed by whole-ecosystem models, indicating perceived food webs have been truncated and species-interactions over simplified. The scaled Δ(15) N framework will greatly improve the accuracy of trophic estimates widely used in ecosystem-based management.

  6. Temperature alters food web body-size structure.

    PubMed

    Gibert, Jean P; DeLong, John P

    2014-08-01

    The increased temperature associated with climate change may have important effects on body size and predator-prey interactions. The consequences of these effects for food web structure are unclear because the relationships between temperature and aspects of food web structure such as predator-prey body-size relationships are unknown. Here, we use the largest reported dataset for marine predator-prey interactions to assess how temperature affects predator-prey body-size relationships among different habitats ranging from the tropics to the poles. We found that prey size selection depends on predator body size, temperature and the interaction between the two. Our results indicate that (i) predator-prey body-size ratios decrease with predator size at below-average temperatures and increase with predator size at above-average temperatures, and (ii) that the effect of temperature on predator-prey body-size structure will be stronger at small and large body sizes and relatively weak at intermediate sizes. This systematic interaction may help to simplify forecasting the potentially complex consequences of warming on interaction strengths and food web stability.

  7. Rescaling the trophic structure of marine food webs

    PubMed Central

    Hussey, Nigel E; MacNeil, M Aaron; McMeans, Bailey C; Olin, Jill A; Dudley, Sheldon FJ; Cliff, Geremy; Wintner, Sabine P; Fennessy, Sean T; Fisk, Aaron T

    2014-01-01

    Measures of trophic position (TP) are critical for understanding food web interactions and human-mediated ecosystem disturbance. Nitrogen stable isotopes (δ15N) provide a powerful tool to estimate TP but are limited by a pragmatic assumption that isotope discrimination is constant (change in δ15N between predator and prey, Δ15N = 3.4‰), resulting in an additive framework that omits known Δ15N variation. Through meta-analysis, we determine narrowing discrimination from an empirical linear relationship between experimental Δ15N and δ15N values of prey consumed. The resulting scaled Δ15N framework estimated reliable TPs of zooplanktivores to tertiary piscivores congruent with known feeding relationships that radically alters the conventional structure of marine food webs. Apex predator TP estimates were markedly higher than currently assumed by whole-ecosystem models, indicating perceived food webs have been truncated and species-interactions over simplified. The scaled Δ15N framework will greatly improve the accuracy of trophic estimates widely used in ecosystem-based management. PMID:24308860

  8. Characteristics of Food Industry Web Sites and "Advergames" Targeting Children

    ERIC Educational Resources Information Center

    Culp, Jennifer; Bell, Robert A.; Cassady, Diana

    2010-01-01

    Objective: To assess the content of food industry Web sites targeting children by describing strategies used to prolong their visits and foster brand loyalty; and to document health-promoting messages on these Web sites. Design: A content analysis was conducted of Web sites advertised on 2 children's networks, Cartoon Network and Nickelodeon. A…

  9. Incorporating food web dynamics into ecological restoration: a modeling approach for river ecosystems.

    PubMed

    Bellmore, J Ryan; Benjamin, Joseph R; Newsom, Michael; Bountry, Jennifer A; Dombroski, Daniel

    2017-04-01

    Restoration is frequently aimed at the recovery of target species, but also influences the larger food web in which these species participate. Effects of restoration on this broader network of organisms can influence target species both directly and indirectly via changes in energy flow through food webs. To help incorporate these complexities into river restoration planning, we constructed a model that links river food web dynamics to in-stream physical habitat and riparian vegetation conditions. We present an application of the model to the Methow River, Washington, USA, a location of on-going restoration aimed at recovering salmon. Three restoration strategies were simulated: riparian vegetation restoration, nutrient augmentation via salmon carcass addition, and side channel reconnection. We also added populations of nonnative aquatic snails and fish to the modeled food web to explore how changes in food web structure mediate responses to restoration. Simulations suggest that side channel reconnection may be a better strategy than carcass addition and vegetation planting for improving conditions for salmon in this river segment. However, modeled responses were strongly sensitive to changes in the structure of the food web. The addition of nonnative snails and fish modified pathways of energy through the food web, which negated restoration improvements. This finding illustrates that forecasting responses to restoration may require accounting for the structure of food webs, and that changes in this structure, as might be expected with the spread of invasive species, could compromise restoration outcomes. Unlike habitat-based approaches to restoration assessment that focus on the direct effects of physical habitat conditions on single species of interest, our approach dynamically links the success of target organisms to the success of competitors, predators, and prey. By elucidating the direct and indirect pathways by which restoration affects target species

  10. Incorporating food web dynamics into ecological restoration: A modeling approach for river ecosystems

    USGS Publications Warehouse

    Bellmore, J. Ryan; Benjamin, Joseph R.; Newsom, Michael; Bountry, Jennifer A.; Dombroski, Daniel

    2017-01-01

    Restoration is frequently aimed at the recovery of target species, but also influences the larger food web in which these species participate. Effects of restoration on this broader network of organisms can influence target species both directly and indirectly via changes in energy flow through food webs. To help incorporate these complexities into river restoration planning we constructed a model that links river food web dynamics to in-stream physical habitat and riparian vegetation conditions. We present an application of the model to the Methow River, Washington (USA), a location of on-going restoration aimed at recovering salmon. Three restoration strategies were simulated: riparian vegetation restoration, nutrient augmentation via salmon carcass addition, and side-channel reconnection. We also added populations of nonnative aquatic snails and fish to the modeled food web to explore how changes in food web structure mediate responses to restoration. Simulations suggest that side-channel reconnection may be a better strategy than carcass addition and vegetation planting for improving conditions for salmon in this river segment. However, modeled responses were strongly sensitive to changes in the structure of the food web. The addition of nonnative snails and fish modified pathways of energy through the food web, which negated restoration improvements. This finding illustrates that forecasting responses to restoration may require accounting for the structure of food webs, and that changes in this structure—as might be expected with the spread of invasive species—could compromise restoration outcomes. Unlike habitat-based approaches to restoration assessment that focus on the direct effects of physical habitat conditions on single species of interest, our approach dynamically links the success of target organisms to the success of competitors, predators, and prey. By elucidating the direct and indirect pathways by which restoration affects target species

  11. A "Bottom-Up" Approach to Food Web Construction

    ERIC Educational Resources Information Center

    Demetriou, Dorita; Korfiatis, Konstantinos; Constantinou, Constantinos

    2009-01-01

    The ability to comprehend trophic (nutritional) relationships and food web dynamics is an essential part of environmental literacy. However, students face severe difficulties in grasping the variety of causal patterns in food webs. We propose a curriculum for comprehending trophic relations in elementary school. The curriculum allows students to…

  12. Predicting the stability of large structured food webs.

    PubMed

    Allesina, Stefano; Grilli, Jacopo; Barabás, György; Tang, Si; Aljadeff, Johnatan; Maritan, Amos

    2015-07-22

    The stability of ecological systems has been a long-standing focus of ecology. Recently, tools from random matrix theory have identified the main drivers of stability in ecological communities whose network structure is random. However, empirical food webs differ greatly from random graphs. For example, their degree distribution is broader, they contain few trophic cycles, and they are almost interval. Here we derive an approximation for the stability of food webs whose structure is generated by the cascade model, in which 'larger' species consume 'smaller' ones. We predict the stability of these food webs with great accuracy, and our approximation also works well for food webs whose structure is determined empirically or by the niche model. We find that intervality and broad degree distributions tend to stabilize food webs, and that average interaction strength has little influence on stability, compared with the effect of variance and correlation.

  13. Predicting the stability of large structured food webs

    PubMed Central

    Allesina, Stefano; Grilli, Jacopo; Barabás, György; Tang, Si; Aljadeff, Johnatan; Maritan, Amos

    2015-01-01

    The stability of ecological systems has been a long-standing focus of ecology. Recently, tools from random matrix theory have identified the main drivers of stability in ecological communities whose network structure is random. However, empirical food webs differ greatly from random graphs. For example, their degree distribution is broader, they contain few trophic cycles, and they are almost interval. Here we derive an approximation for the stability of food webs whose structure is generated by the cascade model, in which ‘larger' species consume ‘smaller' ones. We predict the stability of these food webs with great accuracy, and our approximation also works well for food webs whose structure is determined empirically or by the niche model. We find that intervality and broad degree distributions tend to stabilize food webs, and that average interaction strength has little influence on stability, compared with the effect of variance and correlation. PMID:26198207

  14. Developing a broader scientific foundation for river restoration: Columbia River food webs

    USGS Publications Warehouse

    Naiman, Robert J.; Alldredge, Richard; Beauchamp, David A.; Bisson, Peter A.; Congleton, James; Henny, Charles J.; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N.; Pearcy, William G.; Rieman, Bruce E.; Ruggerone, Gregory T.; Scarnecchia, Dennis; Smouse, Peter E.; Wood, Chris C.

    2012-01-01

    Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure—without explicitly considering food webs—has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

  15. Developing a broader scientific foundation for river restoration: Columbia River food webs

    PubMed Central

    Naiman, Robert J.; Alldredge, J. Richard; Beauchamp, David A.; Bisson, Peter A.; Congleton, James; Henny, Charles J.; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N.; Pearcy, William G.; Rieman, Bruce E.; Ruggerone, Gregory T.; Scarnecchia, Dennis; Smouse, Peter E.; Wood, Chris C.

    2012-01-01

    Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure—without explicitly considering food webs—has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management. PMID:23197837

  16. Food web structure in a harsh glacier-fed river.

    PubMed

    Clitherow, Leonie R; Carrivick, Jonathan L; Brown, Lee E

    2013-01-01

    Glacier retreat is occurring across the world, and associated river ecosystems are expected to respond more rapidly than those in flowing waters in other regions. The river environment directly downstream of a glacier snout is characterised by extreme low water temperature and unstable channel sediments but these habitats may become rarer with widespread glacier retreat. In these extreme environments food web dynamics have been little studied, yet they could offer opportunities to test food web theories using highly resolved food webs owing to their low taxonomic richness. This study examined the interactions of macroinvertebrate and diatom taxa in the Ödenwinkelkees river, Austrian central Alps between 2006 and 2011. The webs were characterised by low taxon richness (13-22), highly connected individuals (directed connectance up to 0.19) and short mean food chain length (2.00-2.36). The dominant macroinvertebrates were members of the Chironomidae genus Diamesa and had an omnivorous diet rich in detritus and diatoms as well as other Chironomidae. Simuliidae (typically detritivorous filterers) had a diet rich in diatoms but also showed evidence of predation on Chironomidae larvae. Food webs showed strong species-averaged and individual size structuring but mass-abundance scaling coefficients were larger than those predicted by metabolic theory, perhaps due to a combination of spatial averaging effects of patchily distributed consumers and resources, and/or consumers deriving unquantified resources from microorganisms attached to the large amounts of ingested rock fragments. Comparison of food web structural metrics with those from 62 published river webs suggest these glacier-fed river food web properties were extreme but in line with general food web scaling predictions, a finding which could prove useful to forecast the effects of anticipated future glacier retreat on the structure of aquatic food webs.

  17. Food marketing on popular children's web sites: a content analysis.

    PubMed

    Alvy, Lisa M; Calvert, Sandra L

    2008-04-01

    In 2006 the Institute of Medicine (IOM) concluded that food marketing was a contributor to childhood obesity in the United States. One recommendation of the IOM committee was for research on newer marketing venues, such as Internet Web sites. The purpose of this cross-sectional study was to answer the IOM's call by examining food marketing on popular children's Web sites. Ten Web sites were selected based on market research conducted by KidSay, which identified favorite sites of children aged 8 to 11 years during February 2005. Using a standardized coding form, these sites were examined page by page for the existence, type, and features of food marketing. Web sites were compared using chi2 analyses. Although food marketing was not pervasive on the majority of the sites, seven of the 10 Web sites contained food marketing. The products marketed were primarily candy, cereal, quick serve restaurants, and snacks. Candystand.com, a food product site, contained a significantly greater amount of food marketing than the other popular children's Web sites. Because the foods marketed to children are not consistent with a healthful diet, nutrition professionals should consider joining advocacy groups to pressure industry to reduce online food marketing directed at youth.

  18. Anti-predator defence and the complexity-stability relationship of food webs.

    PubMed

    Kondoh, Michio

    2007-07-07

    The mechanism for maintaining complex food webs has been a central issue in ecology because theory often predicts that complexity (higher the species richness, more the interactions) destabilizes food webs. Although it has been proposed that prey anti-predator defence may affect the stability of prey-predator dynamics, such studies assumed a limited and relatively simpler variation in the food-web structure. Here, using mathematical models, I report that food-web flexibility arising from prey anti-predator defence enhances community-level stability (community persistence and robustness) in more complex systems and even changes the complexity-stability relationship. The model analysis shows that adaptive predator-specific defence enhances community-level stability under a wide range of food-web complexity levels and topologies, while generalized defence does not. Furthermore, while increasing food-web complexity has minor or negative effects on community-level stability in the absence of defence adaptation, or in the presence of generalized defence, in the presence of predator-specific defence, the connectance-stability relationship may become unimodal. Increasing species richness, in contrast, always lowers community-level stability. The emergence of a positive connectance-stability relationship however necessitates food-web compartmentalization, high defence efficiency and low defence cost, suggesting that it only occurs under a restricted condition.

  19. Food security under climate change

    NASA Astrophysics Data System (ADS)

    Hertel, Thomas W.

    2016-01-01

    Using food prices to assess climate change impacts on food security is misleading. Differential impacts on income require a broader measure of household well-being, such as changes in absolute poverty.

  20. Lateral cascade of indirect effects in food webs with different types of adaptive behavior.

    PubMed

    Kamran-Disfani, Ahmad R; Golubski, Antonio J

    2013-12-21

    It is widely recognized that indirect effects due to adaptive behaviors can have important effects on food webs. One consequence may be to change how readily perturbations propagate through the web, because species' behaviors as well as densities may respond to perturbations. It is not well understood which types of behavior are more likely to facilitate versus inhibit propagation of disturbances through a food web, or how this might be affected by the shape of a food web or the patterns of interaction strengths within it. We model two simple, laterally expanded food webs (one with three trophic levels and one with four), and compare how various adaptive behaviors affect the potential for a newly introduced predator to change the equilibrium densities of distant species. Patterns of changes in response to the introduction were qualitatively similar across most models, as were the ways in which patterns of direct interaction strengths affected those responses. Depending on both the web structure and the specific adaptive behavior, the potential for density changes to propagate through the web could be either increased or diminished relative to the no-behavior model. Two behaviors allowed density changes to propagate through a four-level web that precluded such propagation in the no-behavior model, and each of these two behaviors led to qualitatively different patterns of density changes. In the one model (diet choice) in which density changes were able to propagate in both web structures, patterns of density changes differed qualitatively between webs. Some of our results flowed from the fact that behaviors did not interact directly in the systems we considered, so that indirect effects on distant species had to be at least partly density-mediated. Our models highlight this as an inherent limitation of considering in isolation behaviors that are strictly foraging-related or strictly defense-related, making a case for the value of simultaneously considering multiple

  1. Moving beyond linear food chains: trait-mediated indirect interactions in a rocky intertidal food web.

    PubMed

    Trussell, Geoffrey C; Matassa, Catherine M; Ewanchuk, Patrick J

    2017-03-29

    In simple, linear food chains, top predators can have positive indirect effects on basal resources by causing changes in the traits (e.g. behaviour, feeding rates) of intermediate consumers. Although less is known about trait-mediated indirect interactions (TMIIs) in more complex food webs, it has been suggested that such complexity dampens trophic cascades. We examined TMIIs between a predatory crab (Carcinus maenas) and two ecologically important basal resources, fucoid algae (Ascophyllum nodosum) and barnacles (Semibalanus balanoides), which are consumed by herbivorous (Littorina littorea) and carnivorous (Nucella lapillus) snails, respectively. Because crab predation risk suppresses snail feeding rates, we hypothesized that crabs would also shape direct and indirect interactions among the multiple consumers and resources. We found that the magnitude of TMIIs between the crab and each resource depended on the suite of intermediate consumers present in the food web. Carnivorous snails (Nucella) transmitted TMIIs between crabs and barnacles. However, crab-algae TMIIs were transmitted by both herbivorous (Littorina) and carnivorous (Nucella) snails, and these TMIIs were additive. By causing Nucella to consume fewer barnacles, crab predation risk allowed fucoids that had settled on or between barnacles to remain in the community. Hence, positive interactions between barnacles and algae caused crab-algae TMIIs to be strongest when both consumers were present. Studies of TMIIs in more realistic, reticulate food webs will be necessary for a more complete understanding of how predation risk shapes community dynamics.

  2. The effects of food web structure on ecosystem function exceeds those of precipitation.

    PubMed

    Trzcinski, M Kurtis; Srivastava, Diane S; Corbara, Bruno; Dézerald, Olivier; Leroy, Céline; Carrias, Jean-François; Dejean, Alain; Céréghino, Régis

    2016-09-01

    Ecosystems are being stressed by climate change, but few studies have tested food web responses to changes in precipitation patterns and the consequences to ecosystem function. Fewer still have considered whether results from one geographic region can be applied to other regions, given the degree of community change over large biogeographic gradients. We assembled, in one field site, three types of macroinvertebrate communities within water-filled bromeliads. Two represented food webs containing both a fast filter feeder-microbial and slow detritivore energy channels found in Costa Rica and Puerto Rico, and one represented the structurally simpler food webs in French Guiana, which only contained the fast filter feeder-microbial channel. We manipulated the amount and distribution of rain entering bromeliads and examined how food web structure mediated ecosystem responses to changes in the quantity and temporal distribution of precipitation. Food web structure affected the survival of functional groups in general and ecosystem functions such as decomposition and the production of fine particulate organic matter. Ecosystem processes were more affected by decreased precipitation than were the abundance of micro-organisms and metazoans. In our experiments, the sensitivity of the ecosystem to precipitation change was primarily revealed in the food web dominated by the single filter feeder-microbial channel because other top-down and bottom-up processes were weak or absent. Our results show stronger effects of food web structure than precipitation change per se on the functioning of bromeliad ecosystems. Consequently, we predict that ecosystem function in bromeliads throughout the Americas will be more sensitive to changes in the distribution of species, rather than to the direct effects caused by changes in precipitation.

  3. Isotopic diversity indices: how sensitive to food web structure?

    PubMed

    Brind'Amour, Anik; Dubois, Stanislas F

    2013-01-01

    Recently revisited, the concept of niche ecology has lead to the formalisation of functional and trophic niches using stable isotope ratios. Isotopic diversity indices (IDI) derived from a set of measures assessing the dispersion/distribution of points in the δ-space were recently suggested and increasingly used in the literature. However, three main critics emerge from the use of these IDI: 1) they fail to account for the isotopic sources overlap, 2) some indices are highly sensitive to the number of species and/or the presence of rare species, and 3) the lack of standardization prevents any spatial and temporal comparisons. Using simulations we investigated the ability of six commonly used IDI to discriminate among different trophic food web structures, with a focus on the first two critics. We tested the sensitivity of the IDI to five food web structures along a gradient of sources overlap, varying from two distinct food chains with differentiated sources to two superimposed food chains sharing two sources. For each of the food web structure we varied the number of species (from 10 to 100 species) and the type of species feeding behaviour (i.e. random or selective feeding). Values of IDI were generally larger in food webs with distinct basal sources and tended to decrease as the superimposition of the food chains increased. This was more pronounced when species displayed food preferences in comparison to food webs where species fed randomly on any prey. The number of species composing the food web also had strong effects on the metrics, including those that were supposedly less sensitive to small sample size. In all cases, computing IDI on food webs with low numbers of species always increases the uncertainty of the metrics. A threshold of ~20 species was detected above which several metrics can be safely used.

  4. Dynamics of the Lake Michigan food web, 1970-2000

    USGS Publications Warehouse

    Madenjian, Charles P.; Fahnenstiel, Gary L.; Johengen, Thomas H.; Nalepa, Thomas F.; Vanderploeg, Henry A.; Fleischer, Guy W.; Schneeberger, Philip J.; Benjamin, Darren M.; Smith, Emily B.; Bence, James R.; Rutherford, Edward S.; Lavis, Dennis S.; Robertson, Dale M.; Jude, David J.; Ebener, Mark P.

    2002-01-01

    Herein, we document changes in the Lake Michigan food web between 1970 and 2000 and identify the factors responsible for these changes. Control of sea lamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus) populations in Lake Michigan, beginning in the 1950s and 1960s, had profound effects on the food web. Recoveries of lake whitefish (Coregonus clupeaformis) and burbot (Lota lota) populations, as well as the buildup of salmonine populations, were attributable, at least in part, to sea lamprey control. Based on our analyses, predation by salmonines was primarily responsible for the reduction in alewife abundance during the 1970s and early 1980s. In turn, the decrease in alewife abundance likely contributed to recoveries of deepwater sculpin (Myoxocephalus thompsoni), yellow perch (Perca flavescens), and burbot populations during the 1970s and 1980s. Decrease in the abundance of all three dominant benthic macroinvertebrate groups, including Diporeia, oligochaetes, and sphaeriids, during the 1980s in nearshore waters (50 m deep) of Lake Michigan, was attributable to a decrease in primary production linked to a decline in phosphorus loadings. Continued decrease in Diporeia abundance during the 1990s was associated with the zebra mussel (Dreissena polymorpha) invasion, but specific mechanisms for zebra mussels affecting Diporeia abundance remain unidentified.

  5. Compilation and network analyses of cambrian food webs.

    PubMed

    Dunne, Jennifer A; Williams, Richard J; Martinez, Neo D; Wood, Rachel A; Erwin, Douglas H

    2008-04-29

    A rich body of empirically grounded theory has developed about food webs--the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple "niche model," which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body

  6. Tracking contaminant flux from aquatic to terrestrial food webs

    EPA Science Inventory

    Aquatic insects provide a critical energy subsidy to riparian food webs, yet their role as vectors of contaminants to terrestrial ecosystems is poorly understood. We investigated aquatic resource utilization and contaminant exposure among riparian invertivores (spiders and herpt...

  7. Food webs: reconciling the structure and function of biodiversity.

    PubMed

    Thompson, Ross M; Brose, Ulrich; Dunne, Jennifer A; Hall, Robert O; Hladyz, Sally; Kitching, Roger L; Martinez, Neo D; Rantala, Heidi; Romanuk, Tamara N; Stouffer, Daniel B; Tylianakis, Jason M

    2012-12-01

    The global biodiversity crisis concerns not only unprecedented loss of species within communities, but also related consequences for ecosystem function. Community ecology focuses on patterns of species richness and community composition, whereas ecosystem ecology focuses on fluxes of energy and materials. Food webs provide a quantitative framework to combine these approaches and unify the study of biodiversity and ecosystem function. We summarise the progression of food-web ecology and the challenges in using the food-web approach. We identify five areas of research where these advances can continue, and be applied to global challenges. Finally, we describe what data are needed in the next generation of food-web studies to reconcile the structure and function of biodiversity.

  8. Using food-web theory to conserve ecosystems

    PubMed Central

    McDonald-Madden, E.; Sabbadin, R.; Game, E. T.; Baxter, P. W. J.; Chadès, I.; Possingham, H. P.

    2016-01-01

    Food-web theory can be a powerful guide to the management of complex ecosystems. However, we show that indices of species importance common in food-web and network theory can be a poor guide to ecosystem management, resulting in significantly more extinctions than necessary. We use Bayesian Networks and Constrained Combinatorial Optimization to find optimal management strategies for a wide range of real and hypothetical food webs. This Artificial Intelligence approach provides the ability to test the performance of any index for prioritizing species management in a network. While no single network theory index provides an appropriate guide to management for all food webs, a modified version of the Google PageRank algorithm reliably minimizes the chance and severity of negative outcomes. Our analysis shows that by prioritizing ecosystem management based on the network-wide impact of species protection rather than species loss, we can substantially improve conservation outcomes. PMID:26776253

  9. Regime shifts in marine communities: a complex systems perspective on food web dynamics.

    PubMed

    Yletyinen, Johanna; Bodin, Örjan; Weigel, Benjamin; Nordström, Marie C; Bonsdorff, Erik; Blenckner, Thorsten

    2016-02-24

    Species composition and habitats are changing at unprecedented rates in the world's oceans, potentially causing entire food webs to shift to structurally and functionally different regimes. Despite the severity of these regime shifts, elucidating the precise nature of their underlying processes has remained difficult. We address this challenge with a new analytic approach to detect and assess the relative strength of different driving processes in food webs. Our study draws on complexity theory, and integrates the network-centric exponential random graph modelling (ERGM) framework developed within the social sciences with community ecology. In contrast to previous research, this approach makes clear assumptions of direction of causality and accommodates a dynamic perspective on the emergence of food webs. We apply our approach to analysing food webs of the Baltic Sea before and after a previously reported regime shift. Our results show that the dominant food web processes have remained largely the same, although we detect changes in their magnitudes. The results indicate that the reported regime shift may not be a system-wide shift, but instead involve a limited number of species. Our study emphasizes the importance of community-wide analysis on marine regime shifts and introduces a novel approach to examine food webs.

  10. Climate change and food security.

    PubMed

    Gregory, P J; Ingram, J S I; Brklacich, M

    2005-11-29

    Dynamic interactions between and within the biogeophysical and human environments lead to the production, processing, distribution, preparation and consumption of food, resulting in food systems that underpin food security. Food systems encompass food availability (production, distribution and exchange), food access (affordability, allocation and preference) and food utilization (nutritional and societal values and safety), so that food security is, therefore, diminished when food systems are stressed. Such stresses may be induced by a range of factors in addition to climate change and/or other agents of environmental change (e.g. conflict, HIV/AIDS) and may be particularly severe when these factors act in combination. Urbanization and globalization are causing rapid changes to food systems. Climate change may affect food systems in several ways ranging from direct effects on crop production (e.g. changes in rainfall leading to drought or flooding, or warmer or cooler temperatures leading to changes in the length of growing season), to changes in markets, food prices and supply chain infrastructure. The relative importance of climate change for food security differs between regions. For example, in southern Africa, climate is among the most frequently cited drivers of food insecurity because it acts both as an underlying, ongoing issue and as a short-lived shock. The low ability to cope with shocks and to mitigate long-term stresses means that coping strategies that might be available in other regions are unavailable or inappropriate. In other regions, though, such as parts of the Indo-Gangetic Plain of India, other drivers, such as labour issues and the availability and quality of ground water for irrigation, rank higher than the direct effects of climate change as factors influencing food security. Because of the multiple socio-economic and bio-physical factors affecting food systems and hence food security, the capacity to adapt food systems to reduce their

  11. Food Web Assembly Rules for Generalized Lotka-Volterra Equations.

    PubMed

    Haerter, Jan O; Mitarai, Namiko; Sneppen, Kim

    2016-02-01

    In food webs, many interacting species coexist despite the restrictions imposed by the competitive exclusion principle and apparent competition. For the generalized Lotka-Volterra equations, sustainable coexistence necessitates nonzero determinant of the interaction matrix. Here we show that this requirement is equivalent to demanding that each species be part of a non-overlapping pairing, which substantially constrains the food web structure. We demonstrate that a stable food web can always be obtained if a non-overlapping pairing exists. If it does not, the matrix rank can be used to quantify the lack of niches, corresponding to unpaired species. For the species richness at each trophic level, we derive the food web assembly rules, which specify sustainable combinations. In neighboring levels, these rules allow the higher level to avert competitive exclusion at the lower, thereby incorporating apparent competition. In agreement with data, the assembly rules predict high species numbers at intermediate levels and thinning at the top and bottom. Using comprehensive food web data, we demonstrate how omnivores or parasites with hosts at multiple trophic levels can loosen the constraints and help obtain coexistence in food webs. Hence, omnivory may be the glue that keeps communities intact even under extinction or ecological release of species.

  12. The inverse niche model for food webs with parasites

    USGS Publications Warehouse

    Warren, Christopher P.; Pascual, Mercedes; Lafferty, Kevin D.; Kuris, Armand M.

    2010-01-01

    Although parasites represent an important component of ecosystems, few field and theoretical studies have addressed the structure of parasites in food webs. We evaluate the structure of parasitic links in an extensive salt marsh food web, with a new model distinguishing parasitic links from non-parasitic links among free-living species. The proposed model is an extension of the niche model for food web structure, motivated by the potential role of size (and related metabolic rates) in structuring food webs. The proposed extension captures several properties observed in the data, including patterns of clustering and nestedness, better than does a random model. By relaxing specific assumptions, we demonstrate that two essential elements of the proposed model are the similarity of a parasite's hosts and the increasing degree of parasite specialization, along a one-dimensional niche axis. Thus, inverting one of the basic rules of the original model, the one determining consumers' generality appears critical. Our results support the role of size as one of the organizing principles underlying niche space and food web topology. They also strengthen the evidence for the non-random structure of parasitic links in food webs and open the door to addressing questions concerning the consequences and origins of this structure.

  13. Food Web Assembly Rules for Generalized Lotka-Volterra Equations

    PubMed Central

    Haerter, Jan O.; Mitarai, Namiko; Sneppen, Kim

    2016-01-01

    In food webs, many interacting species coexist despite the restrictions imposed by the competitive exclusion principle and apparent competition. For the generalized Lotka-Volterra equations, sustainable coexistence necessitates nonzero determinant of the interaction matrix. Here we show that this requirement is equivalent to demanding that each species be part of a non-overlapping pairing, which substantially constrains the food web structure. We demonstrate that a stable food web can always be obtained if a non-overlapping pairing exists. If it does not, the matrix rank can be used to quantify the lack of niches, corresponding to unpaired species. For the species richness at each trophic level, we derive the food web assembly rules, which specify sustainable combinations. In neighboring levels, these rules allow the higher level to avert competitive exclusion at the lower, thereby incorporating apparent competition. In agreement with data, the assembly rules predict high species numbers at intermediate levels and thinning at the top and bottom. Using comprehensive food web data, we demonstrate how omnivores or parasites with hosts at multiple trophic levels can loosen the constraints and help obtain coexistence in food webs. Hence, omnivory may be the glue that keeps communities intact even under extinction or ecological release of species. PMID:26828363

  14. Model of carbon cycling in planktonic food webs

    SciTech Connect

    Connolly, J.P.; Coffin, R.B.

    1995-10-01

    A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research. The basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. Bacteria, phytoplankton, three trophic levels of zooplankton, and dissolved organic carbon (DOC) and particulate organic carbon (POC) are modeled. The descriptions of bacterial growth and utilization of the various classes of substrate were treated as universal constants in the application of the model to three distinct ecosystems, ranging from oligotrophic to highly eutrophic. The successful application of the model to these diverse ecosystems supports the basic validity of the description of the microbial food web and the dynamics of carbon flux. The model indicates that the dynamics of bacteria and protozoan zooplankton production govern the rates of oxidation of carbon entering the water column. Explicit consideration of these groups would improve the capability of eutrophication models to predict dissolved oxygen dynamics, particularly when projecting responses to loading changes.

  15. Predator hunting mode influences patterns of prey use from grazing and epigeic food webs.

    PubMed

    Wimp, Gina M; Murphy, Shannon M; Lewis, Danny; Douglas, Margaret R; Ambikapathi, Ramya; Van-Tull, Lie'Ann; Gratton, Claudio; Denno, Robert F

    2013-02-01

    Multichannel omnivory by generalist predators, especially the use of both grazing and epigeic prey, has the potential to increase predator abundance and decrease herbivore populations. However, predator use of the epigeic web (soil surface detritus/microbe/algae consumers) varies considerably for reasons that are poorly understood. We therefore used a stable isotope approach to determine whether prey availability and predator hunting style (active hunting vs. passive web-building) impacted the degree of multichannel omnivory by the two most abundant predators on an intertidal salt marsh, both spiders. We found that carbon isotopic values of herbivores remained constant during the growing season, while values for epigeic feeders became dramatically more enriched such that values for the two webs converged in August. Carbon isotopic values for both spider species remained midway between the two webs as values for epigeic feeders shifted, indicating substantial use of prey from both food webs by both spider species. As the season progressed, prey abundance in the grazing food web increased while prey abundance in the epigeic web remained constant or declined. In response, prey consumption by the web-building spider shifted toward the grazing web to a much greater extent than did consumption by the hunting spider, possibly because passive web-capture is more responsive to changes in prey availability. Although both generalist predator species engaged in multichannel omnivory, hunting mode influenced the extent to which these predators used prey from the grazing and epigeic food webs, and could thereby influence the strength of trophic cascades in both food webs.

  16. Inferring chemical effects on carbon flows in aquatic food webs: methodology and case study.

    PubMed

    De Laender, Frederik; Soetaert, K; Middelburg, J J

    2010-05-01

    The majority of ecotoxicological enclosure experiments monitor species abundances at different chemical concentrations. Here, we present a new modelling approach that estimates changes in food web flows from such data and show that population- and food web level effects are revealed that are not apparent from abundance data alone. For the case of cypermethrin in freshwater enclosures, photosynthesis and excretion (d(-1)) of phytoplankton at 3.643 microg L(-1) cypermethrin were 30% lower and 100% higher than in the control, respectively. The ingestion rate of mesozooplankton (d(-1)) was 6 times higher in the treated enclosures than in the control as food concentration increased with insecticide exposure. With increasing cypermethrin concentrations, nanoflagellates progressively relied on phytoplankton as their main food source, which rendered the food web less stable. We conclude that this tool has excellent potential to analyse the wealth of enclosure data as it only needs species abundance and general constraints.

  17. Ecological-network models link diversity, structure and function in the plankton food-web

    NASA Astrophysics Data System (ADS)

    D’Alelio, Domenico; Libralato, Simone; Wyatt, Timothy; Ribera D’Alcalà, Maurizio

    2016-02-01

    A planktonic food-web model including sixty-three functional nodes (representing auto- mixo- and heterotrophs) was developed to integrate most trophic diversity present in the plankton. The model was implemented in two variants - which we named ‘green’ and ‘blue’ - characterized by opposite amounts of phytoplankton biomass and representing, respectively, bloom and non-bloom states of the system. Taxonomically disaggregated food-webs described herein allowed to shed light on how components of the plankton community changed their trophic behavior in the two different conditions, and modified the overall functioning of the plankton food web. The green and blue food-webs showed distinct organizations in terms of trophic roles of the nodes and carbon fluxes between them. Such re-organization stemmed from switches in selective grazing by both metazoan and protozoan consumers. Switches in food-web structure resulted in relatively small differences in the efficiency of material transfer towards higher trophic levels. For instance, from green to blue states, a seven-fold decrease in phytoplankton biomass translated into only a two-fold decrease in potential planktivorous fish biomass. By linking diversity, structure and function in the plankton food-web, we discuss the role of internal mechanisms, relying on species-specific functionalities, in driving the ‘adaptive’ responses of plankton communities to perturbations.

  18. Trophic magnification of Dechlorane Plus in the marine food webs of Fildes Peninsula in Antarctica.

    PubMed

    Na, Guangshui; Yao, Yao; Gao, Hui; Li, Ruijing; Ge, Linke; Titaley, Ivan A; Santiago-Delgado, Lisandra; Massey Simonich, Staci L

    2017-02-14

    The food web composition, assimilation efficiency of Dechlorane Plus (DP) in food web components, and even extrinsic conditions can affect the trophic biomagnification potentials of DP isomers in food webs. Antarctica ecological system is characterized by the presence of few consumers and simple trophic levels (TLs), which are crucial in discussing the behavior of contaminants. To assess the biomagnification potential of DP in the Antarctic food web, nine representative species were sampled and analyzed from the Fildes Peninsula. Results showed the DP concentrations ranged from 0.25ngg(-1) to 6.81ngg(-1) lipid weight in Antarctic biota and the concentrations of anti-DP and syn-DP showed significantly positive correlations with TLs (p<0.05, ra=0.85; rs=0.81, respectively), suggesting that syn-DP and anti-DP underwent biomagnification and the biomagnification ability of anti-DP was higher than that of syn-DP. The anti-DP fraction (anti-DP/∑DP) (ƒanti=0.23-0.53) of the organisms was lower than that of commercial products (ƒanti=0.68), demonstrating ƒanti was changed during long-range atmospheric transport or stereoselection enrichment through the food web. Furthermore, based on food web magnification factors (FWMF) comparison between DP and polychlorinated biphenyls (PCBs), the biomagnification potential of DP was found to be similar to that of highly chlorinated PCBs.

  19. Ecological-network models link diversity, structure and function in the plankton food-web

    PubMed Central

    D’Alelio, Domenico; Libralato, Simone; Wyatt, Timothy; Ribera d’Alcalà, Maurizio

    2016-01-01

    A planktonic food-web model including sixty-three functional nodes (representing auto- mixo- and heterotrophs) was developed to integrate most trophic diversity present in the plankton. The model was implemented in two variants - which we named ‘green’ and ‘blue’ - characterized by opposite amounts of phytoplankton biomass and representing, respectively, bloom and non-bloom states of the system. Taxonomically disaggregated food-webs described herein allowed to shed light on how components of the plankton community changed their trophic behavior in the two different conditions, and modified the overall functioning of the plankton food web. The green and blue food-webs showed distinct organizations in terms of trophic roles of the nodes and carbon fluxes between them. Such re-organization stemmed from switches in selective grazing by both metazoan and protozoan consumers. Switches in food-web structure resulted in relatively small differences in the efficiency of material transfer towards higher trophic levels. For instance, from green to blue states, a seven-fold decrease in phytoplankton biomass translated into only a two-fold decrease in potential planktivorous fish biomass. By linking diversity, structure and function in the plankton food-web, we discuss the role of internal mechanisms, relying on species-specific functionalities, in driving the ‘adaptive’ responses of plankton communities to perturbations. PMID:26883643

  20. Anthropogenic shift of planktonic food web structure in a coastal lagoon by freshwater flow regulation

    NASA Astrophysics Data System (ADS)

    Hemraj, Deevesh A.; Hossain, A.; Ye, Qifeng; Qin, Jian G.; Leterme, Sophie C.

    2017-03-01

    Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. To reverse the adverse effects of modified freshwater flow, adequate management of discharge is required, especially due to higher water requirements and abstractions for human use. Here, we look at the effects of anthropogenically controlled freshwater flow regimes on the planktonic food web of a Ramsar listed coastal lagoon that is under recovery from degradation. Our results show shifts in water quality and plankton community interactions associated to changes in water flow. These shifts in food web interactions represent modifications in habitat complexity and water quality. At high flow, phytoplankton-zooplankton interactions dominate the food web. Conversely, at low flow, bacteria, viruses and nano/picoplankton interactions are more dominant, with a substantial switch of the food web towards heterotrophy. This switch can be associated with excess organic matter loading, decomposition of dead organisms, and synergistic and antagonistic interactions. We suggest that a lower variability in flow amplitude could be beneficial for the long-term sustaining of water quality and food web interactions, while improving the ecosystem health of systems facing similar stresses as the Coorong.

  1. Ecological-network models link diversity, structure and function in the plankton food-web.

    PubMed

    D'Alelio, Domenico; Libralato, Simone; Wyatt, Timothy; Ribera d'Alcalà, Maurizio

    2016-02-17

    A planktonic food-web model including sixty-three functional nodes (representing auto- mixo- and heterotrophs) was developed to integrate most trophic diversity present in the plankton. The model was implemented in two variants - which we named 'green' and 'blue' - characterized by opposite amounts of phytoplankton biomass and representing, respectively, bloom and non-bloom states of the system. Taxonomically disaggregated food-webs described herein allowed to shed light on how components of the plankton community changed their trophic behavior in the two different conditions, and modified the overall functioning of the plankton food web. The green and blue food-webs showed distinct organizations in terms of trophic roles of the nodes and carbon fluxes between them. Such re-organization stemmed from switches in selective grazing by both metazoan and protozoan consumers. Switches in food-web structure resulted in relatively small differences in the efficiency of material transfer towards higher trophic levels. For instance, from green to blue states, a seven-fold decrease in phytoplankton biomass translated into only a two-fold decrease in potential planktivorous fish biomass. By linking diversity, structure and function in the plankton food-web, we discuss the role of internal mechanisms, relying on species-specific functionalities, in driving the 'adaptive' responses of plankton communities to perturbations.

  2. Anthropogenic shift of planktonic food web structure in a coastal lagoon by freshwater flow regulation

    PubMed Central

    Hemraj, Deevesh A.; Hossain, A.; Ye, Qifeng; Qin, Jian G.; Leterme, Sophie C.

    2017-01-01

    Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. To reverse the adverse effects of modified freshwater flow, adequate management of discharge is required, especially due to higher water requirements and abstractions for human use. Here, we look at the effects of anthropogenically controlled freshwater flow regimes on the planktonic food web of a Ramsar listed coastal lagoon that is under recovery from degradation. Our results show shifts in water quality and plankton community interactions associated to changes in water flow. These shifts in food web interactions represent modifications in habitat complexity and water quality. At high flow, phytoplankton-zooplankton interactions dominate the food web. Conversely, at low flow, bacteria, viruses and nano/picoplankton interactions are more dominant, with a substantial switch of the food web towards heterotrophy. This switch can be associated with excess organic matter loading, decomposition of dead organisms, and synergistic and antagonistic interactions. We suggest that a lower variability in flow amplitude could be beneficial for the long-term sustaining of water quality and food web interactions, while improving the ecosystem health of systems facing similar stresses as the Coorong. PMID:28327643

  3. Anthropogenic shift of planktonic food web structure in a coastal lagoon by freshwater flow regulation.

    PubMed

    Hemraj, Deevesh A; Hossain, A; Ye, Qifeng; Qin, Jian G; Leterme, Sophie C

    2017-03-22

    Anthropogenic modification of aquatic systems has diverse impacts on food web interactions and ecosystem states. To reverse the adverse effects of modified freshwater flow, adequate management of discharge is required, especially due to higher water requirements and abstractions for human use. Here, we look at the effects of anthropogenically controlled freshwater flow regimes on the planktonic food web of a Ramsar listed coastal lagoon that is under recovery from degradation. Our results show shifts in water quality and plankton community interactions associated to changes in water flow. These shifts in food web interactions represent modifications in habitat complexity and water quality. At high flow, phytoplankton-zooplankton interactions dominate the food web. Conversely, at low flow, bacteria, viruses and nano/picoplankton interactions are more dominant, with a substantial switch of the food web towards heterotrophy. This switch can be associated with excess organic matter loading, decomposition of dead organisms, and synergistic and antagonistic interactions. We suggest that a lower variability in flow amplitude could be beneficial for the long-term sustaining of water quality and food web interactions, while improving the ecosystem health of systems facing similar stresses as the Coorong.

  4. Towards a framework for assessment and management of cumulative human impacts on marine food webs.

    PubMed

    Giakoumi, Sylvaine; Halpern, Benjamin S; Michel, Loïc N; Gobert, Sylvie; Sini, Maria; Boudouresque, Charles-François; Gambi, Maria-Cristina; Katsanevakis, Stelios; Lejeune, Pierre; Montefalcone, Monica; Pergent, Gerard; Pergent-Martini, Christine; Sanchez-Jerez, Pablo; Velimirov, Branko; Vizzini, Salvatrice; Abadie, Arnaud; Coll, Marta; Guidetti, Paolo; Micheli, Fiorenza; Possingham, Hugh P

    2015-08-01

    Effective ecosystem-based management requires understanding ecosystem responses to multiple human threats, rather than focusing on single threats. To understand ecosystem responses to anthropogenic threats holistically, it is necessary to know how threats affect different components within ecosystems and ultimately alter ecosystem functioning. We used a case study of a Mediterranean seagrass (Posidonia oceanica) food web and expert knowledge elicitation in an application of the initial steps of a framework for assessment of cumulative human impacts on food webs. We produced a conceptual seagrass food web model, determined the main trophic relationships, identified the main threats to the food web components, and assessed the components' vulnerability to those threats. Some threats had high (e.g., coastal infrastructure) or low impacts (e.g., agricultural runoff) on all food web components, whereas others (e.g., introduced carnivores) had very different impacts on each component. Partitioning the ecosystem into its components enabled us to identify threats previously overlooked and to reevaluate the importance of threats commonly perceived as major. By incorporating this understanding of system vulnerability with data on changes in the state of each threat (e.g., decreasing domestic pollution and increasing fishing) into a food web model, managers may be better able to estimate and predict cumulative human impacts on ecosystems and to prioritize conservation actions.

  5. Hydrological and Biogeochemical Controls on Seasonal and Spatial Differences in Food Webs in the Everglades

    NASA Astrophysics Data System (ADS)

    Kendall, C.; Wankel, S. D.; Bemis, B. E.; Rawlik, P. S.; Krabbenhoft, D. P.; Lange, T.

    2002-05-01

    Stable isotopes can be used to determine the relative trophic positions of biota within a food web, and to improve our understanding of the biomagnification of contaminants. Plants at the base of the food web uptake dissolved organic carbon (DIC) and nitrogen (DIN) for growth, and their tissue reflects the isotopic composition of these sources. Animals then mirror the isotopic composition of the primary producers, as modified by consumer-diet fractionations at successive trophic steps. During 1995-99, we collected algae, macrophyte, invertebrate, and fish samples from 15 USGS sites in the Everglades and analyzed them for d13C and d15N with the goal of characterizing seasonal and spatial differences in food web relations. Carbon isotopes effectively distinguish between two main types of food webs: ones where algae is the dominant base of the food web, which are characteristic of relatively pristine marsh sites with long hydroperiods, and ones where macrophyte debris appears to be a significant source of nutrients, which are apparently characteristic of shorter hydroperiod sites, and nutrient-impacted marshes and canals. There usually is an inverse relation between d13C and d15N of organisms over time, especially in more pristine environments, reflecting seasonal changes in the d13C of DIC and the d15N of DIN. The d13C and d15N of algae also show strong positive correlations with seasonal changes in water levels. This variability is substantially damped up the food chain, probably because of the longer integration times of animals vs. plants. We speculate that these seasonal shifts in water level result in changes in biogeochemical reactions and nutrient levels, with corresponding variations in the d15N and d13C of biota. For example, small changes in water level may change the balance of photosynthesis, bacterial respiration, and atmospheric exchange reactions that control the d13C of DIC. Such changes will probably also affect the d15N of dissolved inorganic N (DIN

  6. Towards a mechanistic understanding of temperature and enrichment effects on species interaction strength, omnivory and food-web structure.

    PubMed

    Sentis, Arnaud; Hemptinne, Jean-Louis; Brodeur, Jacques

    2014-07-01

    Revealing the links between species functional traits, interaction strength and food-web structure is of paramount importance for understanding and predicting the relationships between food-web diversity and stability in a rapidly changing world. However, little is known about the interactive effects of environmental perturbations on individual species, trophic interactions and ecosystem functioning. Here, we combined modelling and laboratory experiments to investigate the effects of warming and enrichment on a terrestrial tritrophic system. We found that the food-web structure is highly variable and switches between exploitative competition and omnivory depending on the effects of temperature and enrichment on foraging behaviour and species interaction strength. Our model contributes to identifying the mechanisms that explain how environmental effects cascade through the food web and influence its topology. We conclude that considering environmental factors and flexible food-web structure is crucial to improve our ability to predict the impacts of global changes on ecosystem diversity and stability.

  7. Eelgrass (Zostera marina) Food Web Structure in Different Environmental Settings

    PubMed Central

    Thormar, Jonas; Hasler-Sheetal, Harald; Baden, Susanne; Boström, Christoffer; Clausen, Kevin Kuhlmann; Krause-Jensen, Dorte; Olesen, Birgit; Rasmussen, Jonas Ribergaard; Svensson, Carl Johan; Holmer, Marianne

    2016-01-01

    This study compares the structure of eelgrass (Zostera marina L.) meadows and associated food webs in two eelgrass habitats in Denmark, differing in exposure, connection to the open sea, nutrient enrichment and water transparency. Meadow structure strongly reflected the environmental conditions in each habitat. The eutrophicated, protected site had higher biomass of filamentous algae, lower eelgrass biomass and shoot density, longer and narrower leaves, and higher above to below ground biomass ratio compared to the less nutrient-enriched and more exposed site. The faunal community composition and food web structure also differed markedly between sites with the eutrophicated, enclosed site having higher biomass of consumers and less complex food web. These relationships resulted in a column shaped biomass distribution of the consumers at the eutrophicated site whereas the less nutrient-rich site showed a pyramidal biomass distribution of consumers coupled with a more diverse consumer community. The differences in meadow and food web structure of the two seagrass habitats, suggest how physical setting may shape ecosystem response and resilience to anthropogenic pressure. We encourage larger, replicated studies to further disentangle the effects of different environmental variables on seagrass food web structure. PMID:26752412

  8. Eelgrass (Zostera marina) Food Web Structure in Different Environmental Settings.

    PubMed

    Thormar, Jonas; Hasler-Sheetal, Harald; Baden, Susanne; Boström, Christoffer; Clausen, Kevin Kuhlmann; Krause-Jensen, Dorte; Olesen, Birgit; Rasmussen, Jonas Ribergaard; Svensson, Carl Johan; Holmer, Marianne

    2016-01-01

    This study compares the structure of eelgrass (Zostera marina L.) meadows and associated food webs in two eelgrass habitats in Denmark, differing in exposure, connection to the open sea, nutrient enrichment and water transparency. Meadow structure strongly reflected the environmental conditions in each habitat. The eutrophicated, protected site had higher biomass of filamentous algae, lower eelgrass biomass and shoot density, longer and narrower leaves, and higher above to below ground biomass ratio compared to the less nutrient-enriched and more exposed site. The faunal community composition and food web structure also differed markedly between sites with the eutrophicated, enclosed site having higher biomass of consumers and less complex food web. These relationships resulted in a column shaped biomass distribution of the consumers at the eutrophicated site whereas the less nutrient-rich site showed a pyramidal biomass distribution of consumers coupled with a more diverse consumer community. The differences in meadow and food web structure of the two seagrass habitats, suggest how physical setting may shape ecosystem response and resilience to anthropogenic pressure. We encourage larger, replicated studies to further disentangle the effects of different environmental variables on seagrass food web structure.

  9. When do evolutionary food web models generate complex networks?

    PubMed

    Allhoff, Korinna T; Drossel, Barbara

    2013-10-07

    Evolutionary foodweb models are used to build food webs by the repeated addition of new species. Population dynamics leads to the extinction or establishment of a newly added species, and possibly to the extinction of other species. The food web structure that emerges after some time is a highly nontrivial result of the evolutionary and dynamical rules. We investigate the evolutionary food web model introduced by Loeuille and Loreau (2005), which characterizes species by their body mass as the only evolving trait. Our goal is to find the reasons behind the model's remarkable robustness and its capability to generate various and stable networks. In contrast to other evolutionary food web models, this model requires neither adaptive foraging nor allometric scaling of metabolic rates with body mass in order to produce complex networks that do not eventually collapse to trivial structures. Our study shows that this is essentially due to the fact that the difference in niche value between predator and prey as well as the feeding range are constrained so that they remain within narrow limits under evolution. Furthermore, competition between similar species is sufficiently strong, so that a trophic level can accommodate several species. We discuss the implications of these findings and argue that the conditions that stabilize other evolutionary food web models have similar effects because they also prevent the occurrence of extreme specialists or extreme generalists that have in general a higher fitness than species with a moderate niche width.

  10. Parasites affect food web structure primarily through increased diversity and complexity.

    PubMed

    Dunne, Jennifer A; Lafferty, Kevin D; Dobson, Andrew P; Hechinger, Ryan F; Kuris, Armand M; Martinez, Neo D; McLaughlin, John P; Mouritsen, Kim N; Poulin, Robert; Reise, Karsten; Stouffer, Daniel B; Thieltges, David W; Williams, Richard J; Zander, Claus Dieter

    2013-01-01

    Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites "dominate" food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites' roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites' feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic organization

  11. Parasites affect food web structure primarily through increased diversity and complexity

    USGS Publications Warehouse

    Dunne, Jennifer A.; Lafferty, Kevin D.; Dobson, Andrew P.; Hechinger, Ryan F.; Kuris, Armand M.; Martinez, Neo D.; McLaughlin, John P.; Mouritsen, Kim N.; Poulin, Robert; Reise, Karsten; Stouffer, Daniel B.; Thieltges, David W.; Williams, Richard J.; Zander, Claus Dieter

    2013-01-01

    Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites ‘‘dominate’’ food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites’ roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites’ feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic

  12. Key features of intertidal food webs that support migratory shorebirds.

    PubMed

    Saint-Béat, Blanche; Dupuy, Christine; Bocher, Pierrick; Chalumeau, Julien; De Crignis, Margot; Fontaine, Camille; Guizien, Katell; Lavaud, Johann; Lefebvre, Sébastien; Montanié, Hélène; Mouget, Jean-Luc; Orvain, Francis; Pascal, Pierre-Yves; Quaintenne, Gwenaël; Radenac, Gilles; Richard, Pierre; Robin, Frédéric; Vézina, Alain F; Niquil, Nathalie

    2013-01-01

    The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain--Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.

  13. Key Features of Intertidal Food Webs That Support Migratory Shorebirds

    PubMed Central

    Saint-Béat, Blanche; Dupuy, Christine; Bocher, Pierrick; Chalumeau, Julien; De Crignis, Margot; Fontaine, Camille; Guizien, Katell; Lavaud, Johann; Lefebvre, Sébastien; Montanié, Hélène; Mouget, Jean-Luc; Orvain, Francis; Pascal, Pierre-Yves; Quaintenne, Gwenaël; Radenac, Gilles; Richard, Pierre; Robin, Frédéric; Vézina, Alain F.; Niquil, Nathalie

    2013-01-01

    The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds. PMID:24204666

  14. Functional group diversity increases with modularity in complex food webs

    PubMed Central

    Montoya, D.; Yallop, M.L.; Memmott, J.

    2015-01-01

    Biodiversity increases the ability of ecosystems to provide multiple functions. Most studies report a positive relationship between species richness and the number of ecosystem functions. However, it is not known whether the number of functional groups is related to the structure of the underlying species interaction network. Here we present food web data from 115 salt marsh islands and show that network structure is associated with the number of functional groups present. Functional group diversity is heterogeneously distributed across spatial scales, with some islands hosting more functional groups than others. Functional groups form modules within the community so that food webs with more modular architectures have more functional group diversity. Further, in communities with different interaction types, modularity can be seen as the multifunctional equivalent of trophic complementarity. Collectively, these findings reveal spatial heterogeneity in the number of functional groups that emerges from patterns in the structure of the food web. PMID:26059871

  15. Functional group diversity increases with modularity in complex food webs.

    PubMed

    Montoya, D; Yallop, M L; Memmott, J

    2015-06-10

    Biodiversity increases the ability of ecosystems to provide multiple functions. Most studies report a positive relationship between species richness and the number of ecosystem functions. However, it is not known whether the number of functional groups is related to the structure of the underlying species interaction network. Here we present food web data from 115 salt marsh islands and show that network structure is associated with the number of functional groups present. Functional group diversity is heterogeneously distributed across spatial scales, with some islands hosting more functional groups than others. Functional groups form modules within the community so that food webs with more modular architectures have more functional group diversity. Further, in communities with different interaction types, modularity can be seen as the multifunctional equivalent of trophic complementarity. Collectively, these findings reveal spatial heterogeneity in the number of functional groups that emerges from patterns in the structure of the food web.

  16. Stability in Real Food Webs: Weak Links in Long Loops

    NASA Astrophysics Data System (ADS)

    Neutel, Anje-Margriet; Heesterbeek, Johan A. P.; de Ruiter, Peter C.

    2002-05-01

    Increasing evidence that the strengths of interactions among populations in biological communities form patterns that are crucial for system stability requires clarification of the precise form of these patterns, how they come about, and why they influence stability. We show that in real food webs, interaction strengths are organized in trophic loops in such a way that long loops contain relatively many weak links. We show and explain mathematically that this patterning enhances stability, because it reduces maximum ``loop weight'' and thus reduces the amount of intraspecific interaction needed for matrix stability. The patterns are brought about by biomass pyramids, a feature common to most ecosystems. Incorporation of biomass pyramids in 104 food-web descriptions reveals that the low weight of the long loops stabilizes complex food webs. Loop-weight analysis could be a useful tool for exploring the structure and organization of complex communities.

  17. Food web dynamics in a seasonally varying wetland

    USGS Publications Warehouse

    DeAngelis, D.L.; Trexler, J.C.; Donalson, D.D.

    2008-01-01

    A spatially explicit model is developed to simulate the small fish community and its underlying food web, in the freshwater marshes of the Everglades. The community is simplified to a few small fish species feeding on periphyton and invertebrates. Other compartments are detritus, crayfish, and a piscivorous fish species. This unit food web model is applied to each of the 10,000 spatial cells on a 100 x 100 pixel landscape. Seasonal variation in water level is assumed and rules are assigned for fish movement in response to rising and falling water levels, which can cause many spatial cells to alternate between flooded and dry conditions. It is shown that temporal variations of water level on a spatially heterogeneous landscape can maintain at least three competing fish species. In addition, these environmental factors can strongly affect the temporal variation of the food web caused by top-down control from the piscivorous fish.

  18. The interplay between population stability and food-web topology predicts the occurrence of motifs in complex food-webs.

    PubMed

    Monteiro, Angelo B; Faria, Lucas Del Bianco

    2016-11-21

    In this paper, we analyzed the occurrence of motifs (modules) in empirical food-webs from different ecosystem types. Differently from previous studies, our analysis did not relied on randomized networks with specific a priori assumptions, which has been demonstrated to produce inconsistent patterns. We aimed to evaluate the interplay between population dynamics and food-web topology, and its consequences to module occurrences in complex food-webs. We evaluated 13 arrangements of three-species modules and 199 arrangements of four-species modules. For each module, we assembled, a corresponding Jacobian predation matrix, and evaluated the arrangements expected to persist after a disturbance in the equilibrium of the populations dynamics (local stability). Our general results were that (1) a limited set of stable arrangements occurs most frequently; (2) the omnivory module is the only three-species module expected to occur both in the stable and unstable region; (3) connectance and omnivory affects the proportion of stable modules; and (4) the type of ecosystem influence the proportion of stable modules. Further, we demonstrated that food-web topology and population dynamics influenced module occurrences in natural communities; presented a function for the ways that local stability increases the probability of module occurrence; and highlighted the use of omnivory degree to access the effect of feeding at more than one trophic level on food-web stability.

  19. Egg boons: central components of marine fatty acid food webs.

    PubMed

    Fuiman, Lee A; Connelly, Tara L; Lowerre-Barbieri, Susan K; McClelland, James W

    2015-02-01

    Food web relationships are traditionally defined in terms of the flow of key elements, such as carbon, nitrogen, and phosphorus, and their role in limiting production. There is growing recognition that availability of important biomolecules, such as fatty acids, may exert controls on secondary production that are not easily explained by traditional element-oriented models. Essential fatty acids (EFAs) are required by most organisms for proper physiological function but are manufactured almost entirely by primary producers. Therefore, the flow of EFAs, especially docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA), through aquatic food webs is critical for ecosystem functioning. A meta-analysis of data on the EFA content of marine organisms reveals that individual eggs of marine animals have exceptionally high concentrations of EFAs, and that superabundances of eggs released in temporally and spatially discrete patches create rich, but temporary, nutritional resources for egg predators, called "egg boons." Mortality rates of fish eggs are disproportionately higher than animals of similar size, and those eggs are consumed by predators, both larger and smaller than the adults that produce the eggs. Thus, egg boons are a major trophic pathway through which EFAs are repackaged and redistributed, and they are among the few pathways that run counter to the main direction of trophic flow. Egg boons can transport EFAs across ecosystems through advection of patches of eggs and spawning migrations of adults. Recognizing the significance of egg boons to aquatic food webs reveals linkages and feedbacks between organisms and environments that have important implications for understanding how food webs vary in time and space. Examples are given of top-down, bottom-up, and lateral control mechanisms that could significantly alter food webs through their effects on eggs. Our results suggest that trophodynamic food web models should include EFAs

  20. Food-Web Structure in Relation to Environmental Gradients and Predator-Prey Ratios in Tank-Bromeliad Ecosystems

    PubMed Central

    Dézerald, Olivier; Leroy, Céline; Corbara, Bruno; Carrias, Jean-François; Pélozuelo, Laurent; Dejean, Alain; Céréghino, Régis

    2013-01-01

    Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators:prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests. PMID:23977128

  1. Food-web structure in relation to environmental gradients and predator-prey ratios in tank-bromeliad ecosystems.

    PubMed

    Dézerald, Olivier; Leroy, Céline; Corbara, Bruno; Carrias, Jean-François; Pélozuelo, Laurent; Dejean, Alain; Céréghino, Régis

    2013-01-01

    Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators:prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests.

  2. Production and food web efficiency decrease as fishing activity increases in a coastal ecosystem

    NASA Astrophysics Data System (ADS)

    Anh, Pham Viet; Everaert, Gert; Goethals, Peter; Vinh, Chu Tien; De Laender, Frederik

    2015-11-01

    Fishing effort in the Vietnamese coastal ecosystem has rapidly increased from the 1990s to the 2000s, with unknown consequences for local ecosystem structure and functioning. Using ecosystem models that integrate fisheries and food webs we found profound differences in the production of six functional groups, the food web efficiency, and eight functional food web indices between the 1990s (low fishing intensity) and the 2000s (high fishing intensity). The functional attributes (e.g. consumption) of high trophic levels (e.g. predators) were lower in the 2000s than in the 1990s while primary production did not vary, causing food web efficiency to decrease up to 40% with time for these groups. The opposite was found for lower trophic levels (e.g. zooplankton): the functional attributes and food web efficiency increased with time (22 and 10% for the functional attributes and food web efficiency, respectively). Total system throughput, a functional food web index, was about 10% higher in the 1990s than in the 2000s, indicating a reduction of the system size and activity with time. The network analyses further indicated that the Vietnamese coastal ecosystem in the 1990s was more developed (higher ascendancy and capacity), more stable (higher overhead) and more mature (higher ratio of ascendancy and capacity) than in the 2000s. In the 1990s the recovery time of the ecosystem was shorter than in 2000s, as indicated by a higher Finn's cycling index in the 1990s (7.8 and 6.5% in 1990s and 2000s, respectively). Overall, our results demonstrate that the Vietnamese coastal ecosystem has experienced profound changes between the 1990s and 2000s, and emphasise the need for a closer inspection of the ecological impact of fishing.

  3. Food caching in orb-web spiders (Araneae: Araneoidea)

    NASA Astrophysics Data System (ADS)

    Champion de Crespigny, Fleur E.; Herberstein, Marie E.; Elgar, Mark A.

    2001-01-01

    Caching or storing surplus prey may reduce the risk of starvation during periods of food deprivation. While this behaviour occurs in a variety of birds and mammals, it is infrequent among invertebrates. However, golden orb-web spiders, Nephila edulis, incorporate a prey cache in their relatively permanent web, which they feed on during periods of food shortage. Heavier spiders significantly reduced weight loss if they were able to access a cache, but lost weight if the cache was removed. The presence or absence of stored prey had no effect on the weight loss of lighter spiders. Furthermore, N. edulis always attacked new prey, irrespective of the number of unprocessed prey in the web. In contrast, females of Argiope keyserlingi, who build a new web every day and do not cache prey, attacked fewer new prey items if some had already been caught. Thus, a necessary pre-adaptation to the evolution of prey caching in orb-web spiders may be a durable or permanent web, such as that constructed by Nephila.

  4. A new modeling approach to define marine ecosystems food-web status with uncertainty assessment

    NASA Astrophysics Data System (ADS)

    Chaalali, Aurélie; Saint-Béat, Blanche; Lassalle, Géraldine; Le Loc'h, François; Tecchio, Samuele; Safi, Georges; Savenkoff, Claude; Lobry, Jérémy; Niquil, Nathalie

    2015-06-01

    Ecosystem models are currently one of the most powerful approaches used to project and analyse the consequences of anthropogenic and climate-driven changes in food web structure and function. The modeling community is however still finding the effective representation of microbial processes as challenging and lacks of techniques for assessing flow uncertainty explicitly. A linear inverse model of the Bay of Biscay continental shelf was built using a Monte Carlo method coupled with a Markov Chain (LIM-MCMC) to characterize the system's trophic food-web status and its associated structural and functional properties. By taking into account the natural variability of ecosystems (and their associated flows) and the lack of data on these environments, this innovative approach enabled the quantification of uncertainties for both estimated flows and derived food-web indices. This uncertainty assessment constituted a real improvement on the existing Ecopath model for the same area and both models results were compared. Our results suggested a food web characterized by main flows at the basis of the food web and a high contribution of primary producers and detritus to the entire system input flows. The developmental stage of the ecosystem was characterized using estimated Ecological Network Analysis (ENA) indices; the LIM-MCMC produced a higher estimate of flow specialization (than the estimate from Ecopath) owing to better consideration of bacterial processes. The results also pointed to a detritus-based food-web with a web-like structure and an intermediate level of internal flow complexity, confirming the results of previous studies. Other current research on ecosystem model comparability is also presented.

  5. Using a Simulation To Teach Food Web Dynamics.

    ERIC Educational Resources Information Center

    Rueter, John G.; Perrin, Nancy A.

    1999-01-01

    Reports on research that tested the effect of using a computer simulation to teach the concept of a food web to nonbiology majors in a large introductory course. Concludes that the use of the simulation resulted in significantly better performance on an open-ended essay question for those students who used the software, particularly for average…

  6. Methylmercury biomagnification in an Arctic pelagic food web.

    PubMed

    Ruus, Anders; Øverjordet, Ida B; Braaten, Hans Fredrik V; Evenset, Anita; Christensen, Guttorm; Heimstad, Eldbjørg S; Gabrielsen, Geir W; Borgå, Katrine

    2015-11-01

    Mercury (Hg) is a toxic element that enters the biosphere from natural and anthropogenic sources, and emitted gaseous Hg enters the Arctic from lower latitudes by long-range transport. In aquatic systems, anoxic conditions favor the bacterial transformation of inorganic Hg to methylmercury (MeHg), which has a greater potential for bioaccumulation than inorganic Hg and is the most toxic form of Hg. The main objective of the present study was to quantify the biomagnification of MeHg in a marine pelagic food web, comprising species of zooplankton, fish, and seabirds, from the Kongsfjorden system (Svalbard, Norway), by use of trophic magnification factors. As expected, tissue concentrations of MeHg increased with increasing trophic level in the food web, though at greater rates than observed in several earlier studies, especially at lower latitudes. There was strong correlation between MeHg and total Hg concentrations through the food web as a whole. The concentration of MeHg in kittiwake decreased from May to October, contributing to seasonal differences in trophic magnification factors. The ecology and physiology of the species comprising the food web in question may have a large influence on the magnitude of the biomagnification. A significant linear relationship was also observed between concentrations of selenium and total Hg in birds but not in zooplankton, suggesting the importance of selenium in Hg detoxification for individuals with high Hg concentrations.

  7. Food Webs and Environmental Disturbance: What's the Connection?

    ERIC Educational Resources Information Center

    Ford, Bob; Smith, Bruce M.

    1994-01-01

    Two professors assert that it is not enough to simply tell students that all living organisms are mutually dependent. Describes an activity that allows students to become members of a food web and results in a greater understanding of and appreciation for the interdependencies of living things. Ideas for extension are provided. (ZWH)

  8. Unravelling the Food Web: Dietary Analysis in Modern Ecology.

    ERIC Educational Resources Information Center

    Calver, M. C.; Porter, B. D.

    1986-01-01

    Presents information that gives a methodological background to the concept of food webs. Stresses the importance of calibrated techniques in ecological research and explains direct methods for studying animal diets. Exercises for gathering first-hand data on bird diets and analyzing secondary data on mammal diets are suggested. (ML)

  9. BENTHOS AS THE BASIS FOR ARCTIC FOOD WEBS

    EPA Science Inventory

    Plankton have traditionally been viewed as the basis for limnetic food webs, with zooplankton acting as a gateway for energy passing between phytoplanktonic primary producers and fish. Often, benthic production is considered to be important primarily in shallow systems or as a su...

  10. NATURAL AND ANTHROPOGENIC FACTORS INFLUENCING FOOD WEB STRUCTURE IN GREAT LAKES COASTAL WETLANDS

    EPA Science Inventory

    We are investigating factors governing the biological organization of Great Lakes coastal wetlands. Food web analyses using stable isotope techniques verify the role of algae as an energetic foundation, and also suggest that fundamental changes occur as a result of anthropogenic ...

  11. FOOD WEB STRUCTURE AS A POTENTIAL INDICATOR OF NUTRIENT ENRICHMENT IN GREAT LAKES COASTAL WETLANDS

    EPA Science Inventory

    Analyses of the food webs of Great Lakes coastal wetlands verify the role of algae as an energetic foundation, and also suggest that fundamental changes occur in response to both natural and anthropogenic influences. We analyzed coastal wetlands with a range of nutrient concentra...

  12. Effects of lake acidification and recovery on the stability of zooplankton food webs

    SciTech Connect

    Locke, A. ); Sprules, W.G. )

    1994-03-01

    The effect of food web structure on community stability and resilience has rarely been examined using empirical data. Yet there is a practical application for such studies insofar as resistance stability determines the ability of a system to adsorb' anthropogenic stress and adjustment stability determines the reversibility of resulting damage. The stability of zooplankton food webs in 46 Precambrian Shield lakes was examined using data collected in the 1970s, when pH ranged from 3.8 to 7.0, and in 1990, when pH had increased by up to two units in some lakes. Acidification overcame resistance stability at pH <5.0, as evidenced by decreases in species richness, numbers of predatory and competitive links, directed connectance, predator generalization, and linkage density, identified by analysis of variance. Adjustment stability was demonstrated by changes in food web attributes in lakes with higher pH in 1990 than in the 1970s. Species richness, numbers of predatory and competitive links, linkage density, and predator generalization all increased relative to the 1970s values. Food web attributes of recovering' lakes were statistically indistinguishable from those of lakes of similar pH that had not been more acidic in the 1970s. Similar trajectors of food web change were followed during environmental degradation and recovery. Planktonic food webs of anthropogenically acidified lakes may eventually recover to resemble their pre-acidification condition, given sufficient time without acidic inputs. Whether adjustment stability is a general feature of anthropogenically stressed systems remains to be determined. 42 refs., 2 figs., 4 tabs.

  13. Assimilation of Diazotrophic Nitrogen into Pelagic Food Webs

    PubMed Central

    Woodland, Ryan J.; Holland, Daryl P.; Beardall, John; Smith, Jonathan; Scicluna, Todd; Cook, Perran L. M.

    2013-01-01

    The fate of diazotrophic nitrogen (ND) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that ND fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable ND (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, ND can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable ND (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which ND was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of ND by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of ND from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of ND to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-ND pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that ND can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes underlying the propagation of ND

  14. DEVELOPMENT OF A STREAM FOOD WEB MODEL CONSTRAINED BY STABLE ISOTOPE DATA

    EPA Science Inventory

    Traditional stream food web studies provide static models of trophic structures. These models provide information about interspecific relationships, but not about material flows through food webs. Traditional ecosystem models developed from budgets or tracers provide quantitative...

  15. Designing an Illustrated Food Web to Teach Ecological Concepts: Challenges and Solutions.

    ERIC Educational Resources Information Center

    Godkin, Celia M.

    1999-01-01

    Argues that food webs are an efficient method through which to communicate the core idea of ecology--that all living things are interconnected. Assesses the challenges and solutions to using illustrated food webs. (Author/CCM)

  16. URBANIZATION ALTERS FATTY ACID CONCENTRATIONS OF STREAM FOOD WEBS IN THE NARRAGANSETT BAY WATERSHED

    EPA Science Inventory

    Urbanization and associated human activities negatively affect stream algal and invertebrate assemblages, likely altering food webs. Our goal was to determine if urbanization affects food web essential fatty acids (EFAs) and if EFAs could be useful ecological indicators in monito...

  17. Dynamics in a three species food-web system

    NASA Astrophysics Data System (ADS)

    Gupta, K.; Gakkhar, S.

    2016-04-01

    In this paper, the dynamics of a three species food-web system is discussed. The food-web comprises of one predator and two logistically growing competing species. The predator species is taking food from one of the competitors with Holling type II functional response. Another competitor is the amensal species for the predator of first species. The system is shown to be positive and bounded. The stability of various axial points, boundary points and interior point has been investigated. The persistence of the system has been studied. Numerical simulation has been performed to show the occurrence of Hopf bifurcation and stable limit cycle about the interior point. The presence of second competitor and its interaction with predator gives more complex dynamics than the simple prey-predator system. The existence of transcritical bifurcation has been established about two axial points. The existence of periodic attractor having period-2 solution has been shown, when amensal coefficient is chosen as bifurcation parameter.

  18. Global Climate Change Interaction Web.

    ERIC Educational Resources Information Center

    Fortner, Rosanne W.

    1998-01-01

    Students investigate the effects of global climate change on life in the Great Lakes region in this activity. Teams working together construct as many links as possible for such factors as rainfall, lake water, evaporation, skiing, zebra mussels, wetlands, shipping, walleye, toxic chemicals, coastal homes, and population. (PVD)

  19. Potential for Biomagnification of Contaminants within Marine and Freshwater Food Webs

    DTIC Science & Technology

    1984-11-01

    Two Marine and One Inland Saltwater Food Webs .............. ...................... ... 97 J 11 Concentrations of Heavy Metals in Animals in Three...in Three Kenya Lake Drainage Systems .......... ... 155 59 DDT and PCB Concentrations in Three California Saltwater Food Webs...biomagnification of Ni in any of three saltwater food webs (Table 10). In the Salton Sea and Newport Bay food webs, Ni concentrations averaged ɘ.03

  20. Food Web Designer: a flexible tool to visualize interaction networks.

    PubMed

    Sint, Daniela; Traugott, Michael

    Species are embedded in complex networks of ecological interactions and assessing these networks provides a powerful approach to understand what the consequences of these interactions are for ecosystem functioning and services. This is mandatory to develop and evaluate strategies for the management and control of pests. Graphical representations of networks can help recognize patterns that might be overlooked otherwise. However, there is a lack of software which allows visualizing these complex interaction networks. Food Web Designer is a stand-alone, highly flexible and user friendly software tool to quantitatively visualize trophic and other types of bipartite and tripartite interaction networks. It is offered free of charge for use on Microsoft Windows platforms. Food Web Designer is easy to use without the need to learn a specific syntax due to its graphical user interface. Up to three (trophic) levels can be connected using links cascading from or pointing towards the taxa within each level to illustrate top-down and bottom-up connections. Link width/strength and abundance of taxa can be quantified, allowing generating fully quantitative networks. Network datasets can be imported, saved for later adjustment and the interaction webs can be exported as pictures for graphical display in different file formats. We show how Food Web Designer can be used to draw predator-prey and host-parasitoid food webs, demonstrating that this software is a simple and straightforward tool to graphically display interaction networks for assessing pest control or any other type of interaction in both managed and natural ecosystems from an ecological network perspective.

  1. Highly resolved early Eocene food webs show development of modern trophic structure after the end-Cretaceous extinction

    PubMed Central

    Dunne, Jennifer A.; Labandeira, Conrad C.; Williams, Richard J.

    2014-01-01

    Generalities of food web structure have been identified for extant ecosystems. However, the trophic organization of ancient ecosystems is unresolved, as prior studies of fossil webs have been limited by low-resolution, high-uncertainty data. We compiled highly resolved, well-documented feeding interaction data for 700 taxa from the 48 million-year-old latest early Eocene Messel Shale, which contains a species assemblage that developed after an interval of protracted environmental and biotal change during and following the end-Cretaceous extinction. We compared the network structure of Messel lake and forest food webs to extant webs using analyses that account for scale dependence of structure with diversity and complexity. The Messel lake web, with 94 taxa, displays unambiguous similarities in structure to extant webs. While the Messel forest web, with 630 taxa, displays differences compared to extant webs, they appear to result from high diversity and resolution of insect–plant interactions, rather than substantive differences in structure. The evidence presented here suggests that modern trophic organization developed along with the modern Messel biota during an 18 Myr interval of dramatic post-extinction change. Our study also has methodological implications, as the Messel forest web analysis highlights limitations of current food web data and models. PMID:24648225

  2. Efficient Web Change Monitoring with Page Digest

    SciTech Connect

    Buttler, D J; Rocco, D; Liu, L

    2004-02-20

    The Internet and the World Wide Web have enabled a publishing explosion of useful online information, which has produced the unfortunate side effect of information overload: it is increasingly difficult for individuals to keep abreast of fresh information. In this paper we describe an approach for building a system for efficiently monitoring changes to Web documents. This paper has three main contributions. First, we present a coherent framework that captures different characteristics of Web documents. The system uses the Page Digest encoding to provide a comprehensive monitoring system for content, structure, and other interesting properties of Web documents. Second, the Page Digest encoding enables improved performance for individual page monitors through mechanisms such as short-circuit evaluation, linear time algorithms for document and structure similarity, and data size reduction. Finally, we develop a collection of sentinel grouping techniques based on the Page Digest encoding to reduce redundant processing in large-scale monitoring systems by grouping similar monitoring requests together. We examine how effective these techniques are over a wide range of parameters and have seen an order of magnitude speed up over existing Web-based information monitoring systems.

  3. Designing Industrial Networks Using Ecological Food Web Metrics.

    PubMed

    Layton, Astrid; Bras, Bert; Weissburg, Marc

    2016-10-18

    Biologically Inspired Design (biomimicry) and Industrial Ecology both look to natural systems to enhance the sustainability and performance of engineered products, systems and industries. Bioinspired design (BID) traditionally has focused on a unit operation and single product level. In contrast, this paper describes how principles of network organization derived from analysis of ecosystem properties can be applied to industrial system networks. Specifically, this paper examines the applicability of particular food web matrix properties as design rules for economically and biologically sustainable industrial networks, using an optimization model developed for a carpet recycling network. Carpet recycling network designs based on traditional cost and emissions based optimization are compared to designs obtained using optimizations based solely on ecological food web metrics. The analysis suggests that networks optimized using food web metrics also were superior from a traditional cost and emissions perspective; correlations between optimization using ecological metrics and traditional optimization ranged generally from 0.70 to 0.96, with flow-based metrics being superior to structural parameters. Four structural food parameters provided correlations nearly the same as that obtained using all structural parameters, but individual structural parameters provided much less satisfactory correlations. The analysis indicates that bioinspired design principles from ecosystems can lead to both environmentally and economically sustainable industrial resource networks, and represent guidelines for designing sustainable industry networks.

  4. The role of cannibalism and contaminant source on bioaccumulation in aquatic food webs.

    PubMed

    Fraser, Alison J; Cahill, Thomas M; Lasenby, David C; Mackay, Donald; Milford, Lynne

    2005-04-01

    Two aspects of bioaccumulation in an aquatic food web are explored. First, the possible implications of cannibalism, including the scavenging of conspecifics, as a factor influencing food web bioaccumulation and biomagnification are explored by examining the behavior of total polychlorinated biphenyls (PCBs) in a simple aquatic food web consisting of plankton, juvenile and adult Mysis relicta, Diporeia, and alewife. From an analysis of trophic transfer efficiencies and food consumption rates, it is concluded that, for M. relicta, a maximum extent of cannibalism in a population is about 10%, although certain individuals may be more cannibalistic. The model suggests that cannibalism and scavenging of dead conspecifics generally result in an increase in concentration by self-biomagnification, but the effect is small and unlikely to exceed 5% on the average. Concentration differences also are likely to result from changes in the relative amounts of the dietary components. Highly cannibalistic individuals may achieve higher levels of bioaccumulation. In extreme cases, the food web model becomes mathematically unstable because of excessive feedback of high concentrations. A major implication is that differences in extent of cannibalism and scavenging probably contribute significantly to natural concentration variation in a population. Second, and more important, is the effect of benthic versus pelagic sources, especially when significant fugacity differences exist between these zones. A simple method is described by which the separate contributions from these sources can be estimated for organisms at higher trophic levels.

  5. Animal diversity and ecosystem functioning in dynamic food webs

    PubMed Central

    Schneider, Florian D.; Brose, Ulrich; Rall, Björn C.; Guill, Christian

    2016-01-01

    Species diversity is changing globally and locally, but the complexity of ecological communities hampers a general understanding of the consequences of animal species loss on ecosystem functioning. High animal diversity increases complementarity of herbivores but also increases feeding rates within the consumer guild. Depending on the balance of these counteracting mechanisms, species-rich animal communities may put plants under top-down control or may release them from grazing pressure. Using a dynamic food-web model with body-mass constraints, we simulate ecosystem functions of 20,000 communities of varying animal diversity. We show that diverse animal communities accumulate more biomass and are more exploitative on plants, despite their higher rates of intra-guild predation. However, they do not reduce plant biomass because the communities are composed of larger, and thus energetically more efficient, plant and animal species. This plasticity of community body-size structure reconciles the debate on the consequences of animal species loss for primary productivity. PMID:27703157

  6. Animal diversity and ecosystem functioning in dynamic food webs.

    PubMed

    Schneider, Florian D; Brose, Ulrich; Rall, Björn C; Guill, Christian

    2016-10-05

    Species diversity is changing globally and locally, but the complexity of ecological communities hampers a general understanding of the consequences of animal species loss on ecosystem functioning. High animal diversity increases complementarity of herbivores but also increases feeding rates within the consumer guild. Depending on the balance of these counteracting mechanisms, species-rich animal communities may put plants under top-down control or may release them from grazing pressure. Using a dynamic food-web model with body-mass constraints, we simulate ecosystem functions of 20,000 communities of varying animal diversity. We show that diverse animal communities accumulate more biomass and are more exploitative on plants, despite their higher rates of intra-guild predation. However, they do not reduce plant biomass because the communities are composed of larger, and thus energetically more efficient, plant and animal species. This plasticity of community body-size structure reconciles the debate on the consequences of animal species loss for primary productivity.

  7. Animal diversity and ecosystem functioning in dynamic food webs

    NASA Astrophysics Data System (ADS)

    Schneider, Florian D.; Brose, Ulrich; Rall, Björn C.; Guill, Christian

    2016-10-01

    Species diversity is changing globally and locally, but the complexity of ecological communities hampers a general understanding of the consequences of animal species loss on ecosystem functioning. High animal diversity increases complementarity of herbivores but also increases feeding rates within the consumer guild. Depending on the balance of these counteracting mechanisms, species-rich animal communities may put plants under top-down control or may release them from grazing pressure. Using a dynamic food-web model with body-mass constraints, we simulate ecosystem functions of 20,000 communities of varying animal diversity. We show that diverse animal communities accumulate more biomass and are more exploitative on plants, despite their higher rates of intra-guild predation. However, they do not reduce plant biomass because the communities are composed of larger, and thus energetically more efficient, plant and animal species. This plasticity of community body-size structure reconciles the debate on the consequences of animal species loss for primary productivity.

  8. Mercury in the Pelagic Food Web of Lake Champlain

    PubMed Central

    Chen, Celia; Kamman, Neil; Shanley, James; Chalmers, Ann; Jackson, Brian; Taylor, Vivien; Smeltzer, Eric; Stangel, Pete; Shambaugh, Angela

    2013-01-01

    Lake Champlain continues to experience mercury contamination resulting in public advisories to limit human consumption of top trophic level fish such as walleye. Prior research suggested that mercury levels in biota could be modified by differences in ecosystem productivity as well as mercury loadings. We investigated relationships between mercury in different trophic levels in Lake Champlain. We measured inorganic and methyl mercury in water, seston, and two size fractions of zooplankton from 13 sites representing a range of nutrient loading conditions and productivity. Biomass varied significantly across lake segments in all measured ecosystem compartments in response to significant differences in nutrient levels. Local environmental factors such as alkalinity influenced the partitioning of mercury between water and seston. Mercury incorporation into biota was influenced by the biomass and mercury content of different ecosystem strata. Pelagic fish tissue mercury was a function of fish length and the size of the mercury pool associated with large zooplankton. We used these observations to parameterize a model of mercury transfers in the Lake Champlain food web that accounts for ecosystem productivity effects. Simulations using the mercury trophic transfer model suggest that reductions of 25 to 75% in summertime dissolved eplimnetic total mercury will likely allow fish tissue mercury concentrations to drop to the target level of 0.3 µg g−1 in a 40-cm fish in all lake segments. Changes in nutrient loading and ecosystem productivity in eutrophic segments may delay any response to reduced dissolved mercury and may result in increases in fish tissue mercury. PMID:22193540

  9. The assembly, collapse and restoration of food webs

    USGS Publications Warehouse

    Dobson, Andy; Allesina, Stefano; Lafferty, Kevin; Pascual, Mercedes

    2009-01-01

    Darwin chose the metaphor of a 'tangled bank' to conclude the 'Origin of species'. Two centuries after Darwin's birth, we are still untangling the complex ecological networks he has pondered. In particular, studies of food webs provide important insights into how natural ecosystems function (Pascual & Dunne 2005). Although the nonlinear interactions between many species creates challenges of scale, resolution of data and significant computational constraints, the last 10 years have seen significant advances built on the earlier classic studies of Cohen, May, Pimm, Polis, Lawton and Yodzis (May 1974; Cohen 1978; Pimm 1982; Briand & Cohen 1984, 1987; Yodzis 1989; Cohen et al. 1990; Pimm et al. 1991; Yodzis & Innes 1992; Yodzis 1998). These gains stem from advances in computing power and the collation of more comprehensive data from a broader array of empirical food webs.

  10. Degree correlations in a dynamically generated model food web

    NASA Astrophysics Data System (ADS)

    Rikvold, Per Arne

    2010-02-01

    We explore aspects of the community structures generated by a simple predator-prey model of biological coevolution, using large-scale kinetic Monte Carlo simulations. The model accounts for interspecies and intraspecies competition for resources, as well as adaptive foraging behavior. It produces a metastable low-diversity phase and a stable high-diversity phase. The structures and joint indegree-outdegree distributions of the food webs generated in the latter phase are discussed.

  11. Mercury biomagnification in the food web of a neotropical stream.

    PubMed

    Kwon, Sae Yun; McIntyre, Peter B; Flecker, Alexander S; Campbell, Linda M

    2012-02-15

    Anthropogenic and natural mercury (Hg) contamination have been a major concern in South America since the early 1900s, but it remains unclear whether Hg levels pose a hazard to human health in regions that lack point sources. We studied Hg biomagnification patterns in the food web of Río Las Marías, an Andean piedmont stream in northern Venezuela, which supports a major subsistence fishery. Mercury concentrations and trophic positions in the food web (based on stable isotopes of nitrogen and carbon) were characterized for 24 fish species representing seven trophic guilds (piscivore, generalized carnivore, omnivore, invertivore, algivore, terrestrial herbivore, detritivore). Mercury showed significant biomagnification through the food web, but vertical trophic position explained little of the variation. Muscle Hg concentrations also increased with body mass across the food web. Trophic guild assignments offered a useful alternative to explicit analysis of vertical trophic position; piscivores showed the highest Hg concentrations and terrestrial herbivores had the lowest. There were no consistent seasonal differences in Hg concentrations within the 5 species sampled during both the wet and dry seasons, suggesting that bioavailability is unaffected by strong seasonal variation in rainfall. From a human health perspective, many medium- to large-bodied species that are commonly eaten had Hg concentrations that exceeded International Marketing Limit (IML) (0.5 μg/g) and World Health Organization (WHO) guidelines (0.2 μg/g) for consumption. We conclude that Hg concentrations may pose a health concern for local subsistence fishermen and their families. Our results suggest a need to perform risk assessment and better understand contaminant levels in subsistence and commercial fisheries even in areas that lack known Hg point sources.

  12. Simulating food web dynamics along a gradient: quantifying human influence.

    PubMed

    Jordán, Ferenc; Gjata, Nerta; Mei, Shu; Yule, Catherine M

    2012-01-01

    Realistically parameterized and dynamically simulated food-webs are useful tool to explore the importance of the functional diversity of ecosystems, and in particular relations between the dynamics of species and the whole community. We present a stochastic dynamical food web simulation for the Kelian River (Borneo). The food web was constructed for six different locations, arrayed along a gradient of increasing human perturbation (mostly resulting from gold mining activities) along the river. Along the river, the relative importance of grazers, filterers and shredders decreases with increasing disturbance downstream, while predators become more dominant in governing eco-dynamics. Human activity led to increased turbidity and sedimentation which adversely impacts primary productivity. Since the main difference between the study sites was not the composition of the food webs (structure is quite similar) but the strengths of interactions and the abundance of the trophic groups, a dynamical simulation approach seemed to be useful to better explain human influence. In the pristine river (study site 1), when comparing a structural version of our model with the dynamical model we found that structurally central groups such as omnivores and carnivores were not the most important ones dynamically. Instead, primary consumers such as invertebrate grazers and shredders generated a greater dynamical response. Based on the dynamically most important groups, bottom-up control is replaced by the predominant top-down control regime as distance downstream and human disturbance increased. An important finding, potentially explaining the poor structure to dynamics relationship, is that indirect effects are at least as important as direct ones during the simulations. We suggest that our approach and this simulation framework could serve systems-based conservation efforts. Quantitative indicators on the relative importance of trophic groups and the mechanistic modeling of eco

  13. Hamiltonian dynamics for complex food webs.

    PubMed

    Kozlov, Vladimir; Vakulenko, Sergey; Wennergren, Uno

    2016-03-01

    We investigate stability and dynamics of large ecological networks by introducing classical methods of dynamical system theory from physics, including Hamiltonian and averaging methods. Our analysis exploits the topological structure of the network, namely the existence of strongly connected nodes (hubs) in the networks. We reveal new relations between topology, interaction structure, and network dynamics. We describe mechanisms of catastrophic phenomena leading to sharp changes of dynamics and hence completely altering the ecosystem. We also show how these phenomena depend on the structure of interaction between species. We can conclude that a Hamiltonian structure of biological interactions leads to stability and large biodiversity.

  14. Hamiltonian dynamics for complex food webs

    NASA Astrophysics Data System (ADS)

    Kozlov, Vladimir; Vakulenko, Sergey; Wennergren, Uno

    2016-03-01

    We investigate stability and dynamics of large ecological networks by introducing classical methods of dynamical system theory from physics, including Hamiltonian and averaging methods. Our analysis exploits the topological structure of the network, namely the existence of strongly connected nodes (hubs) in the networks. We reveal new relations between topology, interaction structure, and network dynamics. We describe mechanisms of catastrophic phenomena leading to sharp changes of dynamics and hence completely altering the ecosystem. We also show how these phenomena depend on the structure of interaction between species. We can conclude that a Hamiltonian structure of biological interactions leads to stability and large biodiversity.

  15. Tracking the autochthonous carbon transfer in stream biofilm food webs.

    PubMed

    Risse-Buhl, Ute; Trefzger, Nicolai; Seifert, Anne-Gret; Schönborn, Wilfried; Gleixner, Gerd; Küsel, Kirsten

    2012-01-01

    Food webs in the rhithral zone rely mainly on allochthonous carbon from the riparian vegetation. However, autochthonous carbon might be more important in open canopy streams. In streams, most of the microbial activity occurs in biofilms, associated with the streambed. We followed the autochthonous carbon transfer toward bacteria and grazing protozoa within a stream biofilm food web. Biofilms that developed in a second-order stream (Thuringia, Germany) were incubated in flow channels under climate-controlled conditions. Six-week-old biofilms received either ¹³C- or ¹²C-labeled CO₂, and uptake into phospholipid fatty acids was followed. The dissolved inorganic carbon of the flow channel water became immediately labeled. In biofilms grown under 8-h light/16-h dark conditions, more than 50% of the labeled carbon was incorporated in biofilm algae, mainly filamentous cyanobacteria, pennate diatoms, and nonfilamentous green algae. A mean of 29% of the labeled carbon reached protozoan grazer. The testate amoeba Pseudodifflugia horrida was highly abundant in biofilms and seemed to be the most important grazer on biofilm bacteria and algae. Hence, stream biofilms dominated by cyanobacteria and algae seem to play an important role in the uptake of CO₂ and transfer of autochthonous carbon through the microbial food web.

  16. Multiple anthropogenic stressors and the structural properties of food webs.

    PubMed

    O'Gorman, Eoin J; Fitch, Jayne E; Crowe, Tasman P

    2012-03-01

    Coastal environments are among the most productive on the planet, providing a wide range of ecosystem services. Development and exploitation mean that they are faced with stresses from a number of anthropogenic sources. Such stresses are typically studied in isolation, but multiple stressors can combine in unexpected ways to alter the structure of ecological systems. Here, we experimentally explore the impacts of inorganic nutrients and organic matter on a range of food web properties. We find that these two stressors combine additively to produce significant increases in connectance and mean food chain length. Such increases are typically associated with enhanced robustness to secondary extinctions and productivity, respectively. Despite these apparent beneficial effects, we find a simplification of web structure in terms of taxon richness and diversity, and altered proportions of basal and top species. These effects are driven by a reduction in community assembly and lower consistency in a range of system properties as a result of the multiple stressors. Consequently, impacted food webs are likely to be more vulnerable to human- or climate-induced perturbations in the long-term.

  17. Successional dynamics in the seasonally forced diamond food web.

    PubMed

    Klausmeier, Christopher A; Litchman, Elena

    2012-07-01

    Plankton seasonal succession is a classic example of nonequilibrium community dynamics. Despite the fact that it has been well studied empirically, it lacks a general quantitative theory. Here we investigate a food web model that includes a resource, two phytoplankton, and a shared grazer-the diamond food web-in a seasonal environment. The model produces a number of successional trajectories that have been widely discussed in the context of the verbal Plankton Ecology Group model of succession, such as a spring bloom of a good competitor followed by a grazer-induced clear-water phase, setting the stage for the late-season dominance of a grazer-resistant species. It also predicts a novel, counterintuitive trajectory where the grazer-resistant species has both early- and late-season blooms. The model often generates regular annual cycles but sometimes produces multiyear cycles or chaos, even with identical forcing each year. Parameterizing the model, we show how the successional trajectory depends on nutrient supply and the length of the growing season, two key parameters that vary among water bodies. This model extends nonequilibrium theory to food webs and is a first step toward a quantitative theory of plankton seasonal succession.

  18. Compartments in a marine food web associated with phylogeny, body mass, and habitat structure.

    PubMed

    Rezende, Enrico L; Albert, Eva M; Fortuna, Miguel A; Bascompte, Jordi

    2009-08-01

    A long-standing question in community ecology is whether food webs are organized in compartments, where species within the same compartment interact frequently among themselves, but show fewer interactions with species from other compartments. Finding evidence for this community organization is important since compartmentalization may strongly affect food web robustness to perturbation. However, few studies have found unequivocal evidence of compartments, and none has quantified the suite of mechanisms generating such a structure. Here, we combine computational tools from the physics of complex networks with phylogenetic statistical methods to show that a large marine food web is organized in compartments, and that body size, phylogeny, and spatial structure are jointly associated with such a compartmentalized structure. Sharks account for the majority of predatory interactions within their compartments. Phylogenetically closely related shark species tend to occupy different compartments and have divergent trophic levels, suggesting that competition may play an important role structuring some of these compartments. Current overfishing of sharks has the potential to change the structural properties, which might eventually affect the stability of the food web.

  19. Reducing Methylmercury Accumulation in the Food Webs of San Francisco Bay and Its Local Watersheds

    PubMed Central

    Davis, J.A.; Looker, R.E.; Yee, D.; Marvin-DiPasquale, M.; Grenier, J.L.; Austin, C.M.; McKee, L.J.; Greenfield, B.K.; Brodberg, R.; Blum, J.D.

    2013-01-01

    from urban runoff. Atmospheric deposition is a lower priority for source control in the Bay Area due to a combination of a lack of major local sources and Hg isotope data indicating it is a secondary contributor to food web MeHg. Internal net production of MeHg is the dominant source of MeHg that enters the food web. Controlling internal net production is the second primary management approach, and has the potential to reduce food web MeHg more effectively and within a much shorter time-frame. MeHg cycling and control opportunities vary by habitat. Controlling net MeHg production and accumulation in the food web of upstream reservoirs and ponds is very promising due to the many features of these ecosystems that can be manipulated. The most feasible control options in tidal marshes relate to the design of flow patterns and subhabitats in restoration projects. Options for controlling MeHg production in open Bay habitat are limited due primarily to the highly dispersed distribution of Hg throughout the ecosystem. Other changes in these habitats may also have a large influence on food web MeHg, including temperature changes due to global warming, sea level rise, food web alterations due to introduced species and other causes, and changes in sediment supply. Other options for reducing or mitigating exposure and risk include controlling bioaccumulation, cleanup of contaminated sites, and reducing other factors (e.g., habitat availability) that limit at risk wildlife populations. PMID:23122771

  20. Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake

    PubMed Central

    Rinta, Päivi; van Hardenbroek, Maarten; Jones, Roger I.; Kankaala, Paula; Rey, Fabian; Szidat, Sönke; Wooller, Matthew J.; Heiri, Oliver

    2016-01-01

    Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s) obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes. PMID:27487044

  1. Carbon flows in the benthic food web at the deep-sea observatory HAUSGARTEN (Fram Strait)

    NASA Astrophysics Data System (ADS)

    van Oevelen, Dick; Bergmann, Melanie; Soetaert, Karline; Bauerfeind, Eduard; Hasemann, Christiane; Klages, Michael; Schewe, Ingo; Soltwedel, Thomas; Budaeva, Nataliya E.

    2011-11-01

    The HAUSGARTEN observatory is located in the eastern Fram Strait (Arctic Ocean) and used as long-term monitoring site to follow changes in the Arctic benthic ecosystem. Linear inverse modelling was applied to decipher carbon flows among the compartments of the benthic food web at the central HAUSGARTEN station (2500 m) based on an empirical data set consisting of data on biomass, prokaryote production, total carbon deposition and community respiration. The model resolved 99 carbon flows among 4 abiotic and 10 biotic compartments, ranging from prokaryotes up to megafauna. Total carbon input was 3.78±0.31 mmol C m -2 d -1, which is a comparatively small fraction of total primary production in the area. The community respiration of 3.26±0.20 mmol C m -2 d -1 is dominated by prokaryotes (93%) and has lower contributions from surface-deposit feeding macro- (1.7%) and suspension feeding megafauna (1.9%), whereas contributions from nematode and other macro- and megabenthic compartments were limited to <1%. The high prokaryotic contribution to carbon processing suggests that functioning of the benthic food web at the central HAUSGARTEN station is comparable to abyssal plain sediments that are characterised by strong energy limitation. Faunal diet compositions suggest that labile detritus is important for deposit-feeding nematodes (24% of their diet) and surface-deposit feeding macrofauna (˜44%), but that semi-labile detritus is more important in the diets of deposit-feeding macro- and megafauna. Dependency indices on these food sources were also calculated as these integrate direct (i.e. direct grazing and predator-prey interactions) and indirect (i.e. longer loops in the food web) pathways in the food web. Projected sea-ice retreats for the Arctic Ocean typically anticipate a decrease in the labile detritus flux to the already food-limited benthic food web. The dependency indices indicate that faunal compartments depend similarly on labile and semi-labile detritus

  2. The food web of a tropical rain forest

    SciTech Connect

    Reagan, D.P.; Waide, R.B.

    1996-12-31

    This book summarizes the natural history and trophic dynamics of a relatively simple tropical rain forest community. The community consists of the plants and animals inhabiting a 40 ha area of forest around the El Verde Field Station in the Luquillo Experimental Forest of Puerto Rico. The understanding is based on three decades (1963 to 1993) of investigations conducted or coordinated by the biologists in the Terrestrial Ecology Division of the University of Puerto Rico (formerly the Center for Energy and Environment Research) and by many visiting scientists who have worked at El Verde. The authors construct a comprehensive food web documenting the relationships among species in this community as a means of organizing the information that`s been collected. Lay-people, students, academics, resource managers, professional scientists, and others interested in the natural history of tropical forests should find points of interest in this book. In addition, ecologists specializing in the study of trophic dynamics are provided with a detailed food web from a biome underrepresented in the available data base and with the interpretations of the importance of this web.

  3. Predator diversity and identity drive interaction strength and trophic cascades in a food web.

    PubMed

    Otto, Sonja B; Berlow, Eric L; Rank, Nathan E; Smiley, John; Brose, Ulrich

    2008-01-01

    Declining predator diversity may drastically affect the biomass and productivity of herbivores and plants. Understanding how changes in predator diversity can propagate through food webs to alter ecosystem function is one of the most challenging ecological research topics today. We studied the effects of predator removal in a simple natural food web in the Sierra Nevada mountains of California (USA). By excluding the predators of the third trophic level of a food web in a full-factorial design, we monitored cascading effects of varying predator diversity and composition on the herbivorous beetle Chrysomela aeneicollis and the willow Salix orestera, which compose the first and second trophic levels of the food web. Decreasing predator diversity increased herbivore biomass and survivorship, and consequently increased the amount of plant biomass consumed via a trophic cascade. Despite this simple linear mean effect of diversity on the strength of the trophic cascade, we found additivity, compensation, and interference in the effects of multiple predators on herbivores and plants. Herbivore survivorship and predator-prey interaction strengths varied with predator diversity, predator identity, and the identity of coexisting predators. Additive effects of predators on herbivores and plants may have been driven by temporal niche separation, whereas compensatory effects and interference occurred among predators with a similar phenology. Together, these results suggest that while the general trends of diversity effects may appear linear and additive, other information about species identity was required to predict the effects of removing individual predators. In a community that is not temporally well-mixed, predator traits such as phenology may help predict impacts of species loss on other species. Information about predator natural history and food web structure may help explain variation in predator diversity effects on trophic cascades and ecosystem function.

  4. Automated discovery of food webs from ecological data using logic-based machine learning.

    PubMed

    Bohan, David A; Caron-Lormier, Geoffrey; Muggleton, Stephen; Raybould, Alan; Tamaddoni-Nezhad, Alireza

    2011-01-01

    Networks of trophic links (food webs) are used to describe and understand mechanistic routes for translocation of energy (biomass) between species. However, a relatively low proportion of ecosystems have been studied using food web approaches due to difficulties in making observations on large numbers of species. In this paper we demonstrate that Machine Learning of food webs, using a logic-based approach called A/ILP, can generate plausible and testable food webs from field sample data. Our example data come from a national-scale Vortis suction sampling of invertebrates from arable fields in Great Britain. We found that 45 invertebrate species or taxa, representing approximately 25% of the sample and about 74% of the invertebrate individuals included in the learning, were hypothesized to be linked. As might be expected, detritivore Collembola were consistently the most important prey. Generalist and omnivorous carabid beetles were hypothesized to be the dominant predators of the system. We were, however, surprised by the importance of carabid larvae suggested by the machine learning as predators of a wide variety of prey. High probability links were hypothesized for widespread, potentially destabilizing, intra-guild predation; predictions that could be experimentally tested. Many of the high probability links in the model have already been observed or suggested for this system, supporting our contention that A/ILP learning can produce plausible food webs from sample data, independent of our preconceptions about "who eats whom." Well-characterised links in the literature correspond with links ascribed with high probability through A/ILP. We believe that this very general Machine Learning approach has great power and could be used to extend and test our current theories of agricultural ecosystem dynamics and function. In particular, we believe it could be used to support the development of a wider theory of ecosystem responses to environmental change.

  5. Automated Discovery of Food Webs from Ecological Data Using Logic-Based Machine Learning

    PubMed Central

    Bohan, David A.; Caron-Lormier, Geoffrey; Muggleton, Stephen; Raybould, Alan; Tamaddoni-Nezhad, Alireza

    2011-01-01

    Networks of trophic links (food webs) are used to describe and understand mechanistic routes for translocation of energy (biomass) between species. However, a relatively low proportion of ecosystems have been studied using food web approaches due to difficulties in making observations on large numbers of species. In this paper we demonstrate that Machine Learning of food webs, using a logic-based approach called A/ILP, can generate plausible and testable food webs from field sample data. Our example data come from a national-scale Vortis suction sampling of invertebrates from arable fields in Great Britain. We found that 45 invertebrate species or taxa, representing approximately 25% of the sample and about 74% of the invertebrate individuals included in the learning, were hypothesized to be linked. As might be expected, detritivore Collembola were consistently the most important prey. Generalist and omnivorous carabid beetles were hypothesized to be the dominant predators of the system. We were, however, surprised by the importance of carabid larvae suggested by the machine learning as predators of a wide variety of prey. High probability links were hypothesized for widespread, potentially destabilizing, intra-guild predation; predictions that could be experimentally tested. Many of the high probability links in the model have already been observed or suggested for this system, supporting our contention that A/ILP learning can produce plausible food webs from sample data, independent of our preconceptions about “who eats whom.” Well-characterised links in the literature correspond with links ascribed with high probability through A/ILP. We believe that this very general Machine Learning approach has great power and could be used to extend and test our current theories of agricultural ecosystem dynamics and function. In particular, we believe it could be used to support the development of a wider theory of ecosystem responses to environmental change. PMID

  6. Food webs of the Delta, Suisun Bay and Suisun Marsh: an update on current understanding and possibilities for management

    USGS Publications Warehouse

    Brown, Larry R.; Kimmerer, Wim J.; Conrad, Louise; Lesmeister, Sarah; Mueller-Solger, Anke

    2017-01-01

    This paper reviews and highlights recent research findings on foodweb processes since an earlier review by Kimmerer et al. (2008). We conduct this review within a conceptual framework of the Delta-Suisun food web, which includes both temporal and spatial components. The temporal component is based on knowledge that the landscape has changed markedly from historical conditions. The spatial component of our framework acknowledges that the food web is not spatially static; it varies regionally and across habitat types within regions. The review highlights the idea of a changing baseline with respect to foodweb function. New research also indicates that interactions between habitat-specific food webs vary across the current landscape. For example, based on early work in the South Delta, the food web associated with submerged aquatic vegetation was thought to provide little support to species of concern; however, data from other regions of the estuary suggest that this conceptual model may not apply across the entire region. Habitat restoration has been proposed as a method of re-establishing historic foodweb processes to support species of concern. Benefits are likely for species that directly access such restored habitats, but are less clear for pelagic species. Several topics require attention to further improve the knowledge of food webs needed to support effective management, including: 1) synthesis of factors responsible for low pelagic biomass; 2) monitoring and research on effects of harmful algal blooms; 3) broadening the scope of long-term monitoring; 4) determining benefits of tidal wetland restoration to species of concern, including evaluations of interactions of habitat-specific food webs; and 5) interdisciplinary analysis and synthesis. The only certainty is that food webs will continue to change in response to the changes in the physical environment and new species invasions.

  7. Bioaccumulation of toxaphene congeners in the lake superior food web

    USGS Publications Warehouse

    Muir, D.C.G.; Whittle, D.M.; De Vault, D. S.; Bronte, C.R.; Karlsson, H.; Backus, S.; Teixeira, C.

    2004-01-01

    The bioaccumulation and biotransformation of toxaphene was examined in the food webs of Lake Superior and Siskiwit Lake (Isle Royale) using congener specific analysis as well as stable isotope ratios of carbon and nitrogen to characterize food webs. Toxaphene concentrations (calculated using technical toxaphene) in lake trout (Salvelinus namaycush) from the western basin of Lake Superior (N = 95) averaged (±SD) 889 ± 896 ng/g wet wt and 60 ± 34 ng/g wet wt in Siskiwit Lake. Major congeners in lake trout were B8-789 (P38), B8-2226 (P44), B9-1679 (P50), and B9-1025 (P62). Toxaphene concentrations were found to vary seasonally, especially in lower food web organisms in Lake Superior and to a lesser extent in Siskiwit Lake. Toxaphene concentrations declined significantly in lake herring (Coregonus artedii), rainbow smelt (Omerus mordax), and slimy sculpin (Cottus cognatus) as well as in zooplankton (> 102 &mn;m) and Mysis (Mysis relicta) between May and October. The seasonal variation may reflect seasonal shifts in the species abundance within the zooplankton community. Trophic magnification factors (TMF) derived from regressions of toxaphene congener concentrations versus δ15N were > 1 for most octa- and nonachlorobornanes in Lake Superior except B8-1413 (P26) and B9-715. Log bioaccumulation factors (BAFs) for toxaphene congeners in lake trout (ng/g lipid/ng/L dissolved) ranged from 4.54 to 9.7 and were significantly correlated with log octanol-water partition coefficients. TMFs observed for total toxaphene and congener B9-1679 in Lake Superior were similar to those in Arctic lakes, as well as to previous studies in the Great Lakes, which suggests that the bioaccumulation behavior of toxaphene is similar in pelagic food webs of large, cold water systems. However, toxaphene concentrations were lower in lake trout from Siskiwit Lake and lakes in northwestern Ontario than in Lake Superior possibly because of shorter food chains and greater reliance on zooplankton or

  8. Food web structure in oil sands reclaimed wetlands.

    PubMed

    Kovalenko, K E; Ciborowski, J J H; Daly, C; Dixon, D G; Farwell, A J; Foote, A L; Frederick, K R; Costa, J M Gardner; Kennedy, K; Liber, K; Roy, M C; Slama, C A; Smits, J E G

    2013-07-01

    Boreal wetlands play an important role in global carbon balance. However, their ecosystem function is threatened by direct anthropogenic disturbance and climate change. Oil sands surface mining in the boreal regions of Western Canada denudes tracts of land of organic materials, leaves large areas in need of reclamation, and generates considerable quantities of extraction process-affected materials. Knowledge and validation of reclamation techniques that lead to self-sustaining wetlands has lagged behind development of protocols for reclaiming terrestrial systems. It is important to know whether wetlands reclaimed with oil sands process materials can be restored to levels equivalent to their original ecosystem function. We approached this question by assessing carbon flows and food web structure in naturally formed and oil sands-affected wetlands constructed in 1970-2004 in the postmining landscape. We evaluated whether a prescribed reclamation strategy, involving organic matter amendment, accelerated reclaimed wetland development, leading to wetlands that were more similar to their natural marsh counterparts than wetlands that were not supplemented with organic matter. We measured compartment standing stocks for bacterioplankton, microbial biofilm, macrophytes, detritus, and zoobenthos; concentrations of dissolved organic carbon and residual naphthenic acids; and microbial production, gas fluxes, and aquatic-terrestrial exports (i.e., aquatic insect emergence). The total biomass of several biotic compartments differed significantly between oil sands and reference wetlands. Submerged macrophyte biomass, macroinvertebrate trophic diversity, and predator biomass and richness were lower in oil sands-affected wetlands than in reference wetlands. There was insufficient evidence to conclude that wetland age and wetland amendment with peat-mineral mix mitigate effects of oil sands waste materials on the fully aquatic biota. Although high variability was observed within

  9. Road Salts as Environmental Constraints in Urban Pond Food Webs

    PubMed Central

    Van Meter, Robin J.; Swan, Christopher M.

    2014-01-01

    Freshwater salinization is an emerging environmental filter in urban aquatic ecosystems that receive chloride road salt runoff from vast expanses of impervious surface cover. Our study was designed to evaluate the effects of chloride contamination on urban stormwater pond food webs through changes in zooplankton community composition as well as density and biomass of primary producers and consumers. From May – July 2009, we employed a 2×2×2 full-factorial design to manipulate chloride concentration (low = 177 mg L−1 Cl−/high = 1067 mg L−1 Cl−), gray treefrog (Hyla versicolor) tadpoles (presence/absence) and source of stormwater pond algae and zooplankton inoculum (low conductance/high conductance urban ponds) in 40, 600-L mesocosms. Road salt did serve as a constraint on zooplankton community structure, driving community divergence between the low and high chloride treatments. Phytoplankton biomass (chlorophyll [a] µg L−1) in the mesocosms was significantly greater for the high conductance inoculum (P<0.001) and in the high chloride treatment (P = 0.046), whereas periphyton biomass was significantly lower in the high chloride treatment (P = 0.049). Gray treefrog tadpole time to metamorphosis did not vary significantly between treatments. However, mass at metamorphosis was greater among tadpoles that experienced a faster than average time to metamorphosis and exposure to high chloride concentrations (P = 0.039). Our results indicate differential susceptibility to chloride salts among algal resources and zooplankton taxa, and further suggest that road salts can act as a significant environmental constraint on urban stormwater pond communities. PMID:24587259

  10. Rainfall and hydrological stability alter the impact of top predators on food web structure and function.

    PubMed

    Marino, Nicholas A C; Srivastava, Diane S; MacDonald, A Andrew M; Leal, Juliana S; Campos, Alice B A; Farjalla, Vinicius F

    2017-02-01

    Climate change will alter the distribution of rainfall, with potential consequences for the hydrological dynamics of aquatic habitats. Hydrological stability can be an important determinant of diversity in temporary aquatic habitats, affecting species persistence and the importance of predation on community dynamics. As such, prey are not only affected by drought-induced mortality but also the risk of predation [a non-consumptive effect (NCE)] and actual consumption by predators [a consumptive effect (CE)]. Climate-induced changes in rainfall may directly, or via altered hydrological stability, affect predator-prey interactions and their cascading effects on the food web, but this has rarely been explored, especially in natural food webs. To address this question, we performed a field experiment using tank bromeliads and their aquatic food web, composed of predatory damselfly larvae, macroinvertebrate prey and bacteria. We manipulated the presence and consumption ability of damselfly larvae under three rainfall scenarios (ambient, few large rainfall events and several small rainfall events), recorded the hydrological dynamics within bromeliads and examined the effects on macroinvertebrate colonization, nutrient cycling and bacterial biomass and turnover. Despite our large perturbations of rainfall, rainfall scenario had no effect on the hydrological dynamics of bromeliads. As a result, macroinvertebrate colonization and nutrient cycling depended on the hydrological stability of bromeliads, with no direct effect of rainfall or predation. In contrast, rainfall scenario determined the direction of the indirect effects of predators on bacteria, driven by both predator CEs and NCEs. These results suggest that rainfall and the hydrological stability of bromeliads had indirect effects on the food web through changes in the CEs and NCEs of predators. We suggest that future studies should consider the importance of the variability in hydrological dynamics among habitats as

  11. Temporal variation in regulation of production in a pelagic food web model

    SciTech Connect

    Bartell, S.M.; Brenkert, A.L.; O'Neill, R.V.; Gardner, R.H.

    1987-01-01

    We examined the implications of differential resource use and predator-prey relations in a seasonal environment, formalized as a pelagic food web model, on temporal changes in the relative importance of bottom-up and top-down structuring of the phytoplankton. Detailed analyses of the model's behavior were used to identify periods when control of production shifted from interspecific interactions among the phytoplankton to cascading trophic interactions.

  12. Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds

    SciTech Connect

    Davis, J.A.; Looker, R.E.; Yee, D.; Marvin-Di Pasquale, M.; Austin, C.M.; McKee, L.J.; Greenfield, B.K.; Brodberg, R.; Blum, J.D.

    2012-11-15

    from urban runoff. Atmospheric deposition is a lower priority for source control in the Bay Area due to a combination of a lack of major local sources. Internal net production of MeHg is the dominant source of MeHg that enters the food web. Controlling internal net production is the second primary management approach, and has the potential to reduce food web MeHg in some habitats more effectively and within a much shorter time-frame. Controlling net MeHg production and accumulation in the food web of upstream reservoirs and ponds is very promising due to the many features of these ecosystems that can be manipulated. The most feasible control options in tidal marshes relate to the design of flow patterns and subhabitats in restoration projects. Options for controlling MeHg production in open Bay habitat are limited due primarily to the highly dispersed distribution of Hg throughout the ecosystem. Other changes in these habitats may also have a large influence on food web MeHg, including temperature changes due to global warming, sea level rise, food web alterations due to introduced species and other causes, and changes in sediment supply. Other options for reducing or mitigating exposure and risk include controlling bioaccumulation, cleanup of contaminated sites, and reducing other factors (e.g., habitat availability) that limit at-risk wildlife populations.

  13. Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds.

    PubMed

    Davis, J A; Looker, R E; Yee, D; Marvin-Di Pasquale, M; Grenier, J L; Austin, C M; McKee, L J; Greenfield, B K; Brodberg, R; Blum, J D

    2012-11-01

    from urban runoff. Atmospheric deposition is a lower priority for source control in the Bay Area due to a combination of a lack of major local sources. Internal net production of MeHg is the dominant source of MeHg that enters the food web. Controlling internal net production is the second primary management approach, and has the potential to reduce food web MeHg in some habitats more effectively and within a much shorter time-frame. Controlling net MeHg production and accumulation in the food web of upstream reservoirs and ponds is very promising due to the many features of these ecosystems that can be manipulated. The most feasible control options in tidal marshes relate to the design of flow patterns and subhabitats in restoration projects. Options for controlling MeHg production in open Bay habitat are limited due primarily to the highly dispersed distribution of Hg throughout the ecosystem. Other changes in these habitats may also have a large influence on food web MeHg, including temperature changes due to global warming, sea level rise, food web alterations due to introduced species and other causes, and changes in sediment supply. Other options for reducing or mitigating exposure and risk include controlling bioaccumulation, cleanup of contaminated sites, and reducing other factors (e.g., habitat availability) that limit at-risk wildlife populations.

  14. River food web response to large-scale riparian zone manipulations.

    PubMed

    Wootton, J Timothy

    2012-01-01

    Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr) goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR) and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks.

  15. River Food Web Response to Large-Scale Riparian Zone Manipulations

    PubMed Central

    Wootton, J. Timothy

    2012-01-01

    Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr) goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR) and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks. PMID:23284786

  16. Microbial Food-Web Drivers in Tropical Reservoirs.

    PubMed

    Domingues, Carolina Davila; da Silva, Lucia Helena Sampaio; Rangel, Luciana Machado; de Magalhães, Leonardo; de Melo Rocha, Adriana; Lobão, Lúcia Meirelles; Paiva, Rafael; Roland, Fábio; Sarmento, Hugo

    2017-04-01

    Element cycling in aquatic systems is driven chiefly by planktonic processes, and the structure of the planktonic food web determines the efficiency of carbon transfer through trophic levels. However, few studies have comprehensively evaluated all planktonic food-web components in tropical regions. The aim of this study was to unravel the top-down controls (metazooplankton community structure), bottom-up controls (resource availability), and hydrologic (water residence time) and physical (temperature) variables that affect different components of the microbial food web (MFW) carbon stock in tropical reservoirs, through structural equation models (SEM). We conducted a field study in four deep Brazilian reservoirs (Balbina, Tucuruí, Três Marias, and Funil) with different trophic states (oligo-, meso-, and eutrophic). We found evidence of a high contribution of the MFW (up to 50% of total planktonic carbon), especially in the less-eutrophic reservoirs (Balbina and Tucuruí). Bottom-up and top-down effects assessed through SEM indicated negative interactions between soluble reactive phosphorus and phototrophic picoplankton (PPP), dissolved inorganic nitrogen, and heterotrophic nanoflagellates (HNF). Copepods positively affected ciliates, and cladocerans positively affected heterotrophic bacteria (HB) and PPP. Higher copepod/cladoceran ratios and an indirect positive effect of copepods on HB might strengthen HB-HNF coupling. We also found low values for the degree of uncoupling (D) and a low HNF/HB ratio compared with literature data (mostly from temperate regions). This study demonstrates the importance of evaluating the whole size spectrum (including microbial compartments) of the different planktonic compartments, in order to capture the complex carbon dynamics of tropical aquatic ecosystems.

  17. Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past.

    PubMed

    Saporiti, Fabiana; Bearhop, Stuart; Silva, Laura; Vales, Damián G; Zenteno, Lisette; Crespo, Enrique A; Aguilar, Alex; Cardona, Luis

    2014-01-01

    The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs.

  18. Longer and Less Overlapping Food Webs in Anthropogenically Disturbed Marine Ecosystems: Confirmations from the Past

    PubMed Central

    Saporiti, Fabiana; Bearhop, Stuart; Silva, Laura; Vales, Damián G.; Zenteno, Lisette; Crespo, Enrique A.; Aguilar, Alex; Cardona, Luis

    2014-01-01

    The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs. PMID:25076042

  19. Parasitism and Food Web Structure in Defoliating Lepidoptera - Parasitoid Communities on Soybean.

    PubMed

    Avalos, D S; Mangeaud, A; Valladares, G R

    2016-12-01

    Food webs are usually regarded as snapshots of community feeding interactions. Here, we describe the yearly and cumulative structure of parasitoid-caterpillar food webs on soybean in central Argentina, analyzing parasitism rates and their variability in relation to parasitoid diversity and food web vulnerability in the system. Lepidoptera larvae were collected along four seasons from soybean crops and reared in laboratory to obtain and identify adults and parasitoids. Eleven species of defoliating Lepidoptera and ten parasitoid species were recorded. Food web statistics showed rather low annual variability, with most variation coefficients in the order of 0.20 and generality showing the most stable values. Parasitism showed the highest variability, which was independent of parasitoid diversity and food web vulnerability, although parasitism rates were negatively related to parasitoid richness. Our study highlights the need to consider food web structure and variability in order to understand the functioning of ecological communities in general and in extensive agricultural ecosystems in particular.

  20. Food-web complexity, meta-community complexity and community stability.

    PubMed

    Mougi, A; Kondoh, M

    2016-04-13

    What allows interacting, diverse species to coexist in nature has been a central question in ecology, ever since the theoretical prediction that a complex community should be inherently unstable. Although the role of spatiality in species coexistence has been recognized, its application to more complex systems has been less explored. Here, using a meta-community model of food web, we show that meta-community complexity, measured by the number of local food webs and their connectedness, elicits a self-regulating, negative-feedback mechanism and thus stabilizes food-web dynamics. Moreover, the presence of meta-community complexity can give rise to a positive food-web complexity-stability effect. Spatiality may play a more important role in stabilizing dynamics of complex, real food webs than expected from ecological theory based on the models of simpler food webs.

  1. Moving up the information food chain: Deploying softbots on the World Wide Web

    SciTech Connect

    Etzioni, O.

    1996-12-31

    I view the World Wide Web as an information food chain. The maze of pages and hyperlinks that comprise the Web are at the very bottom of the chain. The WebCrawlers and Alta Vistas of the world are information herbivores; they graze on Web pages and regurgitate them as searchable indices. Today, most Web users feed near the bottom of the information food chain, but the time is ripe to move up. Since 1991, we have been building information carnivores, which intelligently hunt and feast on herbivores in Unix, on the Internet, and on the Web.

  2. Impacts of elevated terrestrial nutrient loads and temperature on pelagic food-web efficiency and fish production.

    PubMed

    Lefébure, R; Degerman, R; Andersson, A; Larsson, S; Eriksson, L-O; Båmstedt, U; Byström, P

    2013-05-01

    Both temperature and terrestrial organic matter have strong impacts on aquatic food-web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food-web dynamics and food-web efficiency in a plausible future scenario with respect to these abiotic variables in a large-scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food-web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food-web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web.

  3. Application of information theory methods to food web reconstruction

    USGS Publications Warehouse

    Moniz, L.J.; Cooch, E.G.; Ellner, S.P.; Nichols, J.D.; Nichols, J.M.

    2007-01-01

    In this paper we use information theory techniques on time series of abundances to determine the topology of a food web. At the outset, the food web participants (two consumers, two resources) are known; in addition we know that each consumer prefers one of the resources over the other. However, we do not know which consumer prefers which resource, and if this preference is absolute (i.e., whether or not the consumer will consume the non-preferred resource). Although the consumers and resources are identified at the beginning of the experiment, we also provide evidence that the consumers are not resources for each other, and the resources do not consume each other. We do show that there is significant mutual information between resources; the model is seasonally forced and some shared information between resources is expected. Similarly, because the model is seasonally forced, we expect shared information between consumers as they respond to the forcing of the resources. The model that we consider does include noise, and in an effort to demonstrate that these methods may be of some use in other than model data, we show the efficacy of our methods with decreasing time series size; in this particular case we obtain reasonably clear results with a time series length of 400 points. This approaches ecological time series lengths from real systems.

  4. Body size drives allochthony in food webs of tropical rivers.

    PubMed

    Jardine, Timothy D; Rayner, Thomas S; Pettit, Neil E; Valdez, Dominic; Ward, Douglas P; Lindner, Garry; Douglas, Michael M; Bunn, Stuart E

    2017-02-01

    Food web subsidies from external sources ("allochthony") can support rich biological diversity and high secondary and tertiary production in aquatic systems, even those with low rates of primary production. However, animals vary in their degree of dependence on these subsidies. We examined dietary sources for aquatic animals restricted to refugial habitats (waterholes) during the dry season in Australia's wet-dry tropics, and show that allochthony is strongly size dependent. While small-bodied fishes and invertebrates derived a large proportion of their diet from autochthonous sources within the waterhole (phytoplankton, periphyton, or macrophytes), larger animals, including predatory fishes and crocodiles, demonstrated allochthony from seasonally inundated floodplains, coastal zones or the surrounding savanna. Autochthony declined roughly 10% for each order of magnitude increase in body size. The largest animals in the food web, estuarine crocodiles (Crocodylus porosus), derived ~80% of their diet from allochthonous sources. Allochthony enables crocodiles and large predatory fish to achieve high biomass, countering empirically derived expectations for negative density vs. body size relationships. These results highlight the strong degree of connectivity that exists between rivers and their floodplains in systems largely unaffected by river regulation or dams and levees, and how large iconic predators could be disproportionately affected by these human activities.

  5. Coupled predator-prey oscillations in a chaotic food web.

    PubMed

    Benincà, Elisa; Jöhnk, Klaus D; Heerkloss, Reinhard; Huisman, Jef

    2009-12-01

    Coupling of several predator-prey oscillations can generate intriguing patterns of synchronization and chaos. Theory predicts that prey species will fluctuate in phase if predator-prey cycles are coupled through generalist predators, whereas they will fluctuate in anti-phase if predator-prey cycles are coupled through competition between prey species. Here, we investigate predator-prey oscillations in a long-term experiment with a marine plankton community. Wavelet analysis of the species fluctuations reveals two predator-prey cycles that fluctuate largely in anti-phase. The phase angles point at strong competition between the phytoplankton species, but relatively little prey overlap among the zooplankton species. This food web architecture is consistent with the size structure of the plankton community, and generates highly dynamic food webs. Continued alternations in species dominance enable coexistence of the prey species through a non-equilibrium 'killing-the-winner' mechanism, as the system shifts back and forth between the two predator-prey cycles in a chaotic fashion.

  6. Biomagnification of polychlorinated biphenyls through a riverine food web

    SciTech Connect

    Zaranko, D.T.; Kaushik, N.K.; Griffiths, R.W.

    1997-07-01

    From 1989 to 1993, biota collected from Pottersburg Creek, London, ON, Canada were analyzed for total polychlorinated biphenyls (PCBs) and lipids. Data were analyzed by analysis of covariance (ANCOVA) with lipid as the covariate, to investigate station, time, and trophic effects on PCB accumulation in aquatic organisms. All three variables were highly significant. PCB concentrations in biota decreased along the length of the creek away from the point source. PCB concentrations in biota collected in July 1993 were not significantly different from concentrations in biota collected in July 1990, suggesting that sources into the creek have not been alleviated. The relationship between PCBs and lipid for biota from Pottersburg Creek suggests that organisms accumulate PCBs relative to their position in the food web. Fish and leeches occupying the top of the food web accumulated more PCBs than organisms occupying a lower trophic position (crayfish and oligochaetes/chironomids), indicating that biomagnification through trophic transfer (i.e., the uptake of a chemical through ingestion) is the primary mechanism governing contaminant levels in biota and not bioconcentration (i.e, the uptake of a chemical from water).

  7. Impact of biodiversity loss on production in complex marine food webs mitigated by prey-release.

    PubMed

    Fung, Tak; Farnsworth, Keith D; Reid, David G; Rossberg, Axel G

    2015-03-23

    Public concern over biodiversity loss is often rationalized as a threat to ecosystem functioning, but biodiversity-ecosystem functioning (BEF) relations are hard to empirically quantify at large scales. We use a realistic marine food-web model, resolving species over five trophic levels, to study how total fish production changes with species richness. This complex model predicts that BEF relations, on average, follow simple Michaelis-Menten curves when species are randomly deleted. These are shaped mainly by release of fish from predation, rather than the release from competition expected from simpler communities. Ordering species deletions by decreasing body mass or trophic level, representing 'fishing down the food web', accentuates prey-release effects and results in unimodal relationships. In contrast, simultaneous unselective harvesting diminishes these effects and produces an almost linear BEF relation, with maximum multispecies fisheries yield at ≈40% of initial species richness. These findings have important implications for the valuation of marine biodiversity.

  8. Nitrogen addition and warming independently influence the belowground micro-food web in a temperate steppe.

    PubMed

    Li, Qi; Bai, Huahua; Liang, Wenju; Xia, Jianyang; Wan, Shiqiang; van der Putten, Wim H

    2013-01-01

    Climate warming and atmospheric nitrogen (N) deposition are known to influence ecosystem structure and functioning. However, our understanding of the interactive effect of these global changes on ecosystem functioning is relatively limited, especially when it concerns the responses of soils and soil organisms. We conducted a field experiment to study the interactive effects of warming and N addition on soil food web. The experiment was established in 2006 in a temperate steppe in northern China. After three to four years (2009-2010), we found that N addition positively affected microbial biomass and negatively influenced trophic group and ecological indices of soil nematodes. However, the warming effects were less obvious, only fungal PLFA showed a decreasing trend under warming. Interestingly, the influence of N addition did not depend on warming. Structural equation modeling analysis suggested that the direct pathway between N addition and soil food web components were more important than the indirect connections through alterations in soil abiotic characters or plant growth. Nitrogen enrichment also affected the soil nematode community indirectly through changes in soil pH and PLFA. We conclude that experimental warming influenced soil food web components of the temperate steppe less than N addition, and there was little influence of warming on N addition effects under these experimental conditions.

  9. Nitrogen Addition and Warming Independently Influence the Belowground Micro-Food Web in a Temperate Steppe

    PubMed Central

    Li, Qi; Bai, Huahua; Liang, Wenju; Xia, Jianyang; Wan, Shiqiang; van der Putten, Wim H.

    2013-01-01

    Climate warming and atmospheric nitrogen (N) deposition are known to influence ecosystem structure and functioning. However, our understanding of the interactive effect of these global changes on ecosystem functioning is relatively limited, especially when it concerns the responses of soils and soil organisms. We conducted a field experiment to study the interactive effects of warming and N addition on soil food web. The experiment was established in 2006 in a temperate steppe in northern China. After three to four years (2009–2010), we found that N addition positively affected microbial biomass and negatively influenced trophic group and ecological indices of soil nematodes. However, the warming effects were less obvious, only fungal PLFA showed a decreasing trend under warming. Interestingly, the influence of N addition did not depend on warming. Structural equation modeling analysis suggested that the direct pathway between N addition and soil food web components were more important than the indirect connections through alterations in soil abiotic characters or plant growth. Nitrogen enrichment also affected the soil nematode community indirectly through changes in soil pH and PLFA. We conclude that experimental warming influenced soil food web components of the temperate steppe less than N addition, and there was little influence of warming on N addition effects under these experimental conditions. PMID:23544140

  10. Food web structure and the evolution of ecological communities

    NASA Astrophysics Data System (ADS)

    Quince, Christopher; Higgs, Paul G.; McKane, Alan J.

    Simulations of the coevolution of many interacting species are performed using the Webworld model. The model has a realistic set of predator-prey equations that describe the population dynamics of the species for any structure of the food web. The equations account for competition between species for the same resources, and for the diet choice of predators between alternative prey according to an evolutionarily stable strategy. The set of species present undergoes long-term evolution d ue to speciation and extinction events. We summarize results obtained on the macro-evolutionary dynamics of speciations and extinctions, and on the statistical properties of the food webs that are generated by the model. Simulations begin from small numbers of species and build up to larger webs with relatively constant species number on average. The rate of origination and extinction of species are relatively high, but remain roughly balanced throughout the simulations. When a 'parent' species undergoes sp eciation, the 'child' species usually adds to the same trophic level as the parent. The chance of the child species surviving is significantly higher if the parent is on the second or third trophic level than if it is on the first level, most likely due to a wider choice of possible prey for species on higher levels. Addition of a new species sometimes causes extinction of existing species. The parent species has a high probability of extinction because it has strong competition with the new species. Non-pa rental competitors of the new species also have a significantly higher extinction probability than average, as do prey of the new species. Predators of the new species are less likely than average to become extinct.

  11. Fatty acids as biomarkers for food web structure in the eastern North Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Behrens, J.; Aluwihare, L.; Stephens, B. M.

    2015-12-01

    Resulting from a NSF funded REU program at Scripps Institution of Oceanography in 2015, this research utilized gas chromatography-mass spectrometry (GC-MS) to analyze the fatty acid composition of suspended particulate organic matter (POM) and zooplankton (ZP; primarily copepods). Samples analyzed for this study were collected simultaneously from surface waters approximately 9 miles off the coast of San Diego in June 2015. I was testing the hypothesis that essential fatty acids in ZP should reflect their diet, in particular, distinguishing contributions from a microbial versus traditional food web. Food web structure in this region of the ocean has been shown to be sensitive to climate change on inter-annual and longer timescales. Thus, a proxy that identifies restructuring of food webs would be useful for examining the response of ocean ecosystems to future climate change. Lipids were extracted from ZP and POM using a modified Bligh and Dyer method with sonication. Following saponification free fatty acids and other lipids were further purified using column chromatography. Polar functional groups in lipids were then methylated prior to GC-MS analysis. In addition, 2-dimensional GCxGC with time of flight MS was used to distinguish polyunsaturated fatty acid isomers. My poster will present initial findings of shared fatty acids of zooplankton and POM suspended material from the Northern Pacific collection site. Further research will be focused on analyzing the hydrogen isotope composition of fatty acids in zooplankton and suspended DOM obtained at the collection site to further characterize and increase certainty on the role of microbes and phytoplankton in the region's food-web to distinguish prokaryotic and eukaryotic sources.

  12. The paradox of pelagic food webs in the northern Bering Sea—I. Seabird food habits

    NASA Astrophysics Data System (ADS)

    Springer, Alan M.; Murphy, Edward C.; Roseneau, David G.; McRoy, C. Peter; Cooper, Brian A.

    1987-08-01

    Two distinct environmental settings in the Bering Strait region of the northern Bering Sea lead to characteristic pathways of energy flow through primarily pelagic food webs to avian consumers. In Norton Sound, a large, shallow embayment on the northeastern coast, the physical environment is dominated by the discharge of the Yukon River and by a large seasonal temperature signal. Seabirds breeding at Bluff, the largest colony in Norton Sound, number in the order of 5 × 10 4 and require 1.2 × 10 6 g C d -1. Two piscivorous species constitute the bulk of all seabirds there and are supported by a pelagic food web typical of the coastal zone of the Bering and Chukchi seas. This food web also is present around St. Lawrence Island, on the northwestern shelf, and is important to at least one species of seabird there. In addition, and generally more important, St. Lawrence Island is in a biologically rich environment resulting from the northward flow of water that originates along the continental shelf break of the Bering Sea. This flow apparently accounts for the unexpected presence of oceanic zooplankton and a diversity of forage fishes on the shallow northern shelf that support an abundant and taxonomically rich avifauna. In comparison to Norton Sound, breeding seabirds on St. Lawrence Island number in the order of 2 × 10 6, with planktivores consuming about 8 × 10 6 g C d -1 and piscivores consuming about 16 × 10 6 g C d -1.

  13. Networks within networks: floods, droughts, and the assembly of algal-based food webs in a Mediterranean river

    NASA Astrophysics Data System (ADS)

    Power, M. E.; Limm, M.; Finlay, J. C.; Welter, J.; Furey, P.; Lowe, R.; Hondzo, M.; Dietrich, W. E.; Bode, C. A.; National CenterEarth Surface Dynamics

    2011-12-01

    Riverine biota live within several networks. Organisms are embedded in food webs, whose structure and dynamics respond to environmental changes down river drainages. In sunlit rivers, food webs are fueled by attached algae. Primary producer biomass in the Eel River of Northwestern California, as in many sunlit, temperate rivers worldwide, is dominated by the macroalga Cladophora, which grows as a hierarchical, branched network. Cladophora proliferations vastly amplify the ecological surface area and the diversity microhabitats available to microbes. Environmental conditions (light, substrate age or stability, flow, redox gradients) change in partially predictable ways along both Cladophora fronds and river drainage networks, from the frond tips (or headwaters) to their base (or river mouth). We are interested in the ecological and biogeochemical consequences, at the catchment scale, of cross-scale interactions of microbial food webs on Cladophora with macro-organismal food webs, as these change down river drainages. We are beginning to explore how seasonal, hydrologic and macro-consumer control over the production and fate of Cladophora and its epiphytes could mediate ecosystem linkages of the river, its watershed, and nearshore marine ecosystems. Of the four interacting networks we consider, the web of microbial interactions is the most poorly known, and possibly the least hierarchical due to the prevalence of metabolic processing chains (waste products of some members become resources for others) and mutualisms.

  14. Cross-ecosystem impacts of stream pollution reduce resource and contaminant flux to riparian food webs

    USGS Publications Warehouse

    Kraus, Johanna M.; Schmidt, Travis S.; Walters, David; Wanty, Richard B.; Zuellig, Robert E.; Wolf, Ruth E.

    2014-01-01

    The effects of aquatic contaminants are propagated across ecosystem boundaries by aquatic insects that export resources and contaminants to terrestrial food webs; however, the mechanisms driving these effects are poorly understood. We examined how emergence, contaminant concentration, and total contaminant flux by adult aquatic insects changed over a gradient of bioavailable metals in streams and how these changes affected riparian web-building spiders. Insect emergence decreased 97% over the metal gradient, whereas metal concentrations in adult insects changed relatively little. As a result, total metal exported by insects (flux) was lowest at the most contaminated streams, declining 96% among sites. Spiders were affected by the decrease in prey biomass, but not by metal exposure or metal flux to land in aquatic prey. Aquatic insects are increasingly thought to increase exposure of terrestrial consumers to aquatic contaminants, but stream metals reduce contaminant flux to riparian consumers by strongly impacting the resource linkage. Our results demonstrate the importance of understanding the contaminant-specific effects of aquatic pollutants on adult insect emergence and contaminant accumulation in adults to predict impacts on terrestrial food webs.

  15. Cross-ecosystem impacts of stream pollution reduce resource and contaminant flux to riparian food webs.

    PubMed

    Kraus, Johanna M; Schmidt, Travis S; Walters, David M; Wanty, Richard B; Zuellig, Robert E; Wolf, Ruth E

    2014-03-01

    The effects of aquatic contaminants are propagated across ecosystem boundaries by aquatic insects that export resources and contaminants to terrestrial food webs; however, the mechanisms driving these effects are poorly understood. We examined how emergence, contaminant concentration, and total contaminant flux by adult aquatic insects changed over a gradient of bioavailable metals in streams and how these changes affected riparian web-building spiders. Insect emergence decreased 97% over the metal gradient, whereas metal concentrations in adult insects changed relatively little. As a result, total metal exported by insects (flux) was lowest at the most contaminated streams, declining 96% among sites. Spiders were affected by the decrease in prey biomass, but not by metal exposure or metal flux to land in aquatic prey. Aquatic insects are increasingly thought to increase exposure of terrestrial consumers to aquatic contaminants, but stream metals reduce contaminant flux to riparian consumers by strongly impacting the resource linkage. Our results demonstrate the importance of understanding the contaminant-specific effects of aquatic pollutants on adult insect emergence and contaminant accumulation in adults to predict impacts on terrestrial food webs.

  16. Disruption of the lower food web in Lake Ontario: Did it affect alewife growth or condition?

    USGS Publications Warehouse

    O'Gorman, R.; Prindle, S.E.; Lantry, J.R.; Lantry, B.F.

    2008-01-01

    From the early 1980s to the late 1990s, a succession of non-native invertebrates colonized Lake Ontario and the suite of consequences caused by their colonization became known as "food web disruption". For example, the native burrowing amphipod Diporeia spp., a key link in the profundal food web, declined to near absence, exotic predaceous cladocerans with long spines proliferated, altering the zooplankton community, and depth distributions of fishes shifted. These changes had the potential to affect growth and condition of planktivorous alewife Alosa pseudoharengus, the most abundant fish in the lake. To determine if food web disruption affected alewife, we used change-point analysis to examine alewife growth and adult alewife condition during 1976-2006 and analysis-of-variance to determine if values between change points differed significantly. There were no change points in growth during the first year of life. Of three change points in growth during the second year of life, one coincided with the shift in springtime distribution of alewife to deeper water but it was not associated with a significant change in growth. After the second year of life, no change points in growth were evident, although growth in the third year of life spiked in those years when Bythotrephes, the largest of the exotic cladocerans, was abundant suggesting that it was a profitable prey item for age-2 fish. We detected two change points in condition of adult alewife in fall, but the first occurred in 1981, well before disruption began. A second change point occurred in 2003, well after disruption began. After the springtime distribution of alewife shifted deeper during 1992-1994, growth in the first two years of life became more variable, and growth in years of life two and older became correlated (P < 0.05). In conclusion, food web disruption had no negative affect on growth and condition of alewife in Lake Ontario although it appears to have resulted in growth in the first two years of

  17. Spatial scales of carbon flow in a river food web

    USGS Publications Warehouse

    Finlay, J.C.; Khandwala, S.; Power, M.E.

    2002-01-01

    Spatial extents of food webs that support stream and river consumers are largely unknown, but such information is essential for basic understanding and management of lotic ecosystems. We used predictable variation in algal ??13C with water velocity, and measurements of consumer ??13C and ??15N to examine carbon flow and trophic structure in food webs of the South Fork Eel River in Northern California. Analyses of ??13C showed that the most abundant macroinvertebrate groups (collector-gatherers and scrapers) relied on algae from local sources within their riffle or shallow pool habitats. In contrast, filter-feeding invertebrates in riffles relied in part on algal production derived from upstream shallow pools. Riffle invertebrate predators also relied in part on consumers of pool-derived algal carbon. One abundant taxon drifting from shallow pools and riffles (baetid mayflies) relied on algal production derived from the habitats from which they dispersed. The trophic linkage from pool algae to riffle invertebrate predators was thus mediated through either predation on pool herbivores dispersing into riffles, or on filter feeders. Algal production in shallow pool habitats dominated the resource base of vertebrate predators in all habitats at the end of the summer. We could not distinguish between the trophic roles of riffle algae and terrestrial detritus, but both carbon sources appeared to play minor roles for vertebrate consumers. In shallow pools, small vertebrates, including three-spined stickleback (Gasterosteus aculeatus), roach (Hesperoleucas symmetricus), and rough-skinned newts (Taricha granulosa), relied on invertebrate prey derived from local pool habitats. During the most productive summer period, growth of all size classes of steelhead and resident rainbow trout (Oncorhynchus mykiss) in all habitats (shallow pools, riffles, and deep unproductive pools) was largely derived from algal production in shallow pools. Preliminary data suggest that the strong

  18. The response of the soil microbial food web to extreme rainfall under different plant systems

    PubMed Central

    Sun, Feng; Pan, Kaiwen; Tariq, Akash; Zhang, Lin; Sun, Xiaoming; Li, Zilong; Wang, Sizhong; Xiong, Qinli; Song, Dagang; Olatunji, Olusanya Abiodun

    2016-01-01

    An agroforestry experiment was conducted that involved four planting systems: monoculture of the focal species Zanthoxylum bungeanum and mixed cultures of Z. bungeanum and Capsicum annuum, Z. bungeanum and Medicago sativa and Z. bungeanum and Glycine max. Soil microbial food web (microorganisms and nematodes) was investigated under manipulated extreme rainfall in the four planting systems to assess whether presence of neighbor species alleviated the magnitude of extreme rainfall on nutrient uptake of the focal species by increasing the stability of soil food web. Our results indicate that in the focal species and G. max mixed culture, leaf nitrogen contents of the focal species were higher than in the monoculture and in the other mixed cultures under extreme rainfall. This result was mainly due to the significant increase under extreme rainfall of G. max species root biomass, resulting in enhanced microbial resistance and subsequent net nitrogen mineralization rate and leaf nitrogen uptake for the focal species. Differences in functional traits of neighbors had additive effects and led to a marked divergence of soil food-web resistance and nutrient uptake of the focal species. Climate change can indirectly alleviate focal species via its influence on their neighbors. PMID:27874081

  19. Metamorphosis alters contaminants and chemical tracers in insects: implications for food webs.

    PubMed

    Kraus, Johanna M; Walters, David M; Wesner, Jeff S; Stricker, Craig A; Schmidt, Travis S; Zuellig, Robert E

    2014-09-16

    Insects are integral to most freshwater and terrestrial food webs, but due to their accumulation of environmental pollutants they are also contaminant vectors that threaten reproduction, development, and survival of consumers. Metamorphosis from larvae to adult can cause large chemical changes in insects, altering contaminant concentrations and fractionation of chemical tracers used to establish contaminant biomagnification in food webs, but no framework exists for predicting and managing these effects. We analyzed data from 39 studies of 68 analytes (stable isotopes and contaminants), and found that metamorphosis effects varied greatly. δ(15)N, widely used to estimate relative trophic position in biomagnification studies, was enriched by ∼ 1‰ during metamorphosis, while δ(13)C used to estimate diet, was similar in larvae and adults. Metals and polycyclic aromatic hydrocarbons (PAHs) were predominantly lost during metamorphosis leading to ∼ 2 to 125-fold higher larval concentrations and higher exposure risks for predators of larvae compared to predators of adults. In contrast, manufactured organic contaminants (such as polychlorinated biphenyls) were retained and concentrated in adults, causing up to ∼ 3-fold higher adult concentrations and higher exposure risks to predators of adult insects. Both food web studies and contaminant management and mitigation strategies need to consider how metamorphosis affects the movement of materials between habitats and ecosystems, with special regard for aquatic-terrestrial linkages.

  20. Metamorphosis alters contaminants and chemical tracers in insects: implications for food webs

    USGS Publications Warehouse

    Kraus, Johanna M.; Walters, David M.; Wesner, Jeff S.; Stricker, Craig A.; Schmidt, Travis S.; Zuellig, Robert E.

    2014-01-01

    Insects are integral to most freshwater and terrestrial food webs, but due to their accumulation of environmental pollutants they are also contaminant vectors that threaten reproduction, development, and survival of consumers. Metamorphosis from larvae to adult can cause large chemical changes in insects, altering contaminant concentrations and fractionation of chemical tracers used to establish contaminant biomagnification in food webs, but no framework exists for predicting and managing these effects. We analyzed data from 39 studies of 68 analytes (stable isotopes and contaminants), and found that metamorphosis effects varied greatly. δ15N, widely used to estimate relative trophic position in biomagnification studies, was enriched by 1‰ during metamorphosis, while δ13C used to estimate diet, was similar in larvae and adults. Metals and polycyclic aromatic hydrocarbons (PAHs) were predominantly lost during metamorphosis leading to 2 to 125-fold higher larval concentrations and higher exposure risks for predators of larvae compared to predators of adults. In contrast, manufactured organic contaminants (such as polychlorinated biphenyls) were retained and concentrated in adults, causing up to 3-fold higher adult concentrations and higher exposure risks to predators of adult insects. Both food web studies and contaminant management and mitigation strategies need to consider how metamorphosis affects the movement of materials between habitats and ecosystems, with special regard for aquatic-terrestrial linkages.

  1. The response of the soil microbial food web to extreme rainfall under different plant systems

    NASA Astrophysics Data System (ADS)

    Sun, Feng; Pan, Kaiwen; Tariq, Akash; Zhang, Lin; Sun, Xiaoming; Li, Zilong; Wang, Sizhong; Xiong, Qinli; Song, Dagang; Olatunji, Olusanya Abiodun

    2016-11-01

    An agroforestry experiment was conducted that involved four planting systems: monoculture of the focal species Zanthoxylum bungeanum and mixed cultures of Z. bungeanum and Capsicum annuum, Z. bungeanum and Medicago sativa and Z. bungeanum and Glycine max. Soil microbial food web (microorganisms and nematodes) was investigated under manipulated extreme rainfall in the four planting systems to assess whether presence of neighbor species alleviated the magnitude of extreme rainfall on nutrient uptake of the focal species by increasing the stability of soil food web. Our results indicate that in the focal species and G. max mixed culture, leaf nitrogen contents of the focal species were higher than in the monoculture and in the other mixed cultures under extreme rainfall. This result was mainly due to the significant increase under extreme rainfall of G. max species root biomass, resulting in enhanced microbial resistance and subsequent net nitrogen mineralization rate and leaf nitrogen uptake for the focal species. Differences in functional traits of neighbors had additive effects and led to a marked divergence of soil food-web resistance and nutrient uptake of the focal species. Climate change can indirectly alleviate focal species via its influence on their neighbors.

  2. Evolution mediates the effects of apex predation on aquatic food webs.

    PubMed

    Urban, Mark C

    2013-07-22

    Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance.

  3. Evolution mediates the effects of apex predation on aquatic food webs

    PubMed Central

    Urban, Mark C.

    2013-01-01

    Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance. PMID:23720548

  4. Food and Beverage Brands that Market to Children and Adolescents on the Internet: A Content Analysis of Branded Web Sites

    ERIC Educational Resources Information Center

    Henry, Anna E.; Story, Mary

    2009-01-01

    Objective: To identify food and beverage brand Web sites featuring designated children's areas, assess marketing techniques present on those industry Web sites, and determine nutritional quality of branded food items marketed to children. Design: Systematic content analysis of food and beverage brand Web sites and nutrient analysis of food and…

  5. The probabilistic niche model reveals substantial variation in the niche structure of empirical food webs.

    PubMed

    Williams, Richard J; Purves, Drew W

    2011-09-01

    The structure of food webs, complex networks of interspecies feeding interactions, plays a crucial role in ecosystem resilience and function, and understanding food web structure remains a central problem in ecology. Previous studies have shown that key features of empirical food webs can be reproduced by low-dimensional "niche" models. Here we examine the form and variability of food web niche structure by fitting a probabilistic niche model to 37 empirical food webs, a much larger number of food webs than used in previous studies. The model relaxes previous assumptions about parameter distributions and hierarchy and returns parameter estimates for each species in each web. The model significantly outperforms previous niche model variants and also performs well for several webs where a body-size-based niche model performs poorly, implying that traits other than body size are important in structuring these webs' niche space. Parameter estimates frequently violate previous models' assumptions: in 19 of 37 webs, parameter values are not significantly hierarchical, 32 of 37 webs have nonuniform niche value distributions, and 15 of 37 webs lack a correlation between niche width and niche position. Extending the model to a two-dimensional niche space yields networks with a mixture of one- and two-dimensional niches and provides a significantly better fit for webs with a large number of species and links. These results confirm that food webs are strongly niche-structured but reveal substantial variation in the form of the niche structuring, a result with fundamental implications for ecosystem resilience and function.

  6. Global multi-level analysis of the 'scientific food web'.

    PubMed

    Mazloumian, Amin; Helbing, Dirk; Lozano, Sergi; Light, Robert P; Börner, Katy

    2013-01-01

    We introduce a network-based index analyzing excess scientific production and consumption to perform a comprehensive global analysis of scholarly knowledge production and diffusion on the level of continents, countries, and cities. Compared to measures of scientific production and consumption such as number of publications or citation rates, our network-based citation analysis offers a more differentiated picture of the 'ecosystem of science'. Quantifying knowledge flows between 2000 and 2009, we identify global sources and sinks of knowledge production. Our knowledge flow index reveals, where ideas are born and consumed, thereby defining a global 'scientific food web'. While Asia is quickly catching up in terms of publications and citation rates, we find that its dependence on knowledge consumption has further increased.

  7. Shifts in the trophic base of intermittent stream food webs

    USGS Publications Warehouse

    Dekar, Matthew P.; Magoulick, Daniel D.; Huxel, G.R.

    2009-01-01

    Understanding spatial and temporal variation in the trophic base of stream food webs is critical for predicting population and community stability, and ecosystem function. We used stable isotope ratios (13C/12C, and 15N/14N) to characterize the trophic base of two streams in the Ozark Mountains of northwest Arkansas, U.S.A. We predicted that autochthonous resources would be more important during the spring and summer and allochthonous resources would be more important in the winter due to increased detritus inputs from the riparian zone during autumn leaf drop. We predicted that stream communities would demonstrate increased reliance on autochthonous resources at sites with larger watersheds and greater canopy openness. The study was conducted at three low-order sites in the Mulberry River Drainage (watershed area range: 81-232 km2) seasonally in 2006 and 2007. We used circular statistics to examine community-wide shifts in isotope space among fish and invertebrate consumers in relation to basal resources, including detritus and periphyton. Mixing models were used to quantify the relative contribution of autochthonous and allochthonous energy sources to individual invertebrate consumers. Significant isotopic shifts occurred but results varied by season and site indicating substantial variation in the trophic base of stream food webs. In terms of temporal variation, consumers shifted toward periphyton in the summer during periods of low discharge, but results varied during the interval between summer and winter. Our results did not demonstrate increased reliance on periphyton with increasing watershed area or canopy openness, and detritus was important at all the sites. In our study, riffle-pool geomorphology likely disrupted the expected spatial pattern and stream drying likely impacted the availability and distribution of basal resources.

  8. Biological vs. Physical Mixing Effects on Benthic Food Web Dynamics

    PubMed Central

    Braeckman, Ulrike; Provoost, Pieter; Moens, Tom; Soetaert, Karline; Middelburg, Jack J.; Vincx, Magda; Vanaverbeke, Jan

    2011-01-01

    Biological particle mixing (bioturbation) and solute transfer (bio-irrigation) contribute extensively to ecosystem functioning in sediments where physical mixing is low. Macrobenthos transports oxygen and organic matter deeper into the sediment, thereby likely providing favourable niches to lower trophic levels (i.e., smaller benthic animals such as meiofauna and bacteria) and thus stimulating mineralisation. Whether this biological transport facilitates fresh organic matter assimilation by the metazoan lower part of the food web through niche establishment (i.e., ecosystem engineering) or rather deprives them from food sources, is so far unclear. We investigated the effects of the ecosystem engineers Lanice conchilega (bio-irrigator) and Abra alba (bioturbator) compared to abiotic physical mixing events on survival and food uptake of nematodes after a simulated phytoplankton bloom. The 13C labelled diatom Skeletonema costatum was added to 4 treatments: (1) microcosms containing the bioturbator, (2) microcosms containing the bio-irrigator, (3) control microcosms and (4) microcosms with abiotic manual surface mixing. Nematode survival and subsurface peaks in nematode density profiles were most pronounced in the bio-irrigator treatment. However, nematode specific uptake (Δδ13C) of the added diatoms was highest in the physical mixing treatment, where macrobenthos was absent and the diatom 13C was homogenised. Overall, nematodes fed preferentially on bulk sedimentary organic material rather than the added diatoms. The total C budget (µg C m−2), which included TO13C remaining in the sediment, respiration, nematode and macrobenthic uptake, highlighted the limited assimilation by the metazoan benthos and the major role of bacterial respiration. In summary, bioturbation and especially bio-irrigation facilitated the lower trophic levels mainly over the long-term through niche establishment. Since the freshly added diatoms represented only a limited food source for

  9. Food web de-synchronization in England's largest lake: an assessment based on multiple phenological metrics.

    PubMed

    Thackeray, Stephen J; Henrys, Peter A; Feuchtmayr, Heidrun; Jones, Ian D; Maberly, Stephen C; Winfield, Ian J

    2013-12-01

    Phenological changes have been observed globally for marine, freshwater and terrestrial species, and are an important element of the global biological 'fingerprint' of climate change. Differences in rates of change could desynchronize seasonal species interactions within a food web, threatening ecosystem functioning. Quantification of this risk is hampered by the rarity of long-term data for multiple interacting species from the same ecosystem and by the diversity of possible phenological metrics, which vary in their ecological relevance to food web interactions. We compare phenological change for phytoplankton (chlorophyll a), zooplankton (Daphnia) and fish (perch, Perca fluviatilis) in two basins of Windermere over 40 years and determine whether change has differed among trophic levels, while explicitly accounting for among-metric differences in rates of change. Though rates of change differed markedly among the nine metrics used, seasonal events shifted earlier for all metrics and trophic levels: zooplankton advanced most, and fish least, rapidly. Evidence of altered synchrony was found in both lake basins, when combining information from all phenological metrics. However, comparisons based on single metrics did not consistently detect this signal. A multimetric approach showed that across trophic levels, earlier phenological events have been associated with increasing water temperature. However, for phytoplankton and zooplankton, phenological change was also associated with changes in resource availability. Lower silicate, and higher phosphorus, concentrations were associated with earlier phytoplankton growth, and earlier phytoplankton growth was associated with earlier zooplankton growth. The developing trophic mismatch detected between the dominant fish species in Windermere and important zooplankton food resources may ultimately affect fish survival and portend significant impacts upon ecosystem functioning. We advocate that future studies on phenological

  10. High-resolution food webs based on nitrogen isotopic composition of amino acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Food webs are known to have myriad trophic links between resource and consumer species. However, since the difficulties associated with characterizing the trophic position of organisms—particularly omnivores and higher-order consumers—have remained a major problem in food web ecology, our knowledge ...

  11. Comparison of the structure of lower and upper estuary food webs for Yaquina Bay (OR)

    EPA Science Inventory

    Food web models can be used to estimate effects of water quality, habitat distribution or species loss on productivity, carbon flow and ecosystem service production in Pacific NW estuaries. Here we present a comparison of floral and faunal data used to parameterize food web mode...

  12. Benthic versus Planktonic Foundations of Three Lake Superior Coastal Food Webs

    EPA Science Inventory

    The structure of aquatic food webs can provide information on system function, trophic dynamics and, potentially, responses to anthropogenic stressors. Stable isotope analyses in a Lake Superior coastal wetland (Allouez Bay, WI, USA) revealed that the food web was based upon carb...

  13. IMPORTANCE OF TEMPERATURE IN MODELLING PCB BIOACCUMULATION IN THE LAKE MICHIGAN FOOD WEB

    EPA Science Inventory

    In most food web models, the exposure temperature of a food web is typically defined using a single spatial compartment. This essentially assumes that the predator and prey are exposed to the same temperature. However, in a large water body such as Lake Michigan, due to the spati...

  14. Can You Build It? Using Manipulatives to Assess Student Understanding of Food-Web Concepts

    ERIC Educational Resources Information Center

    Grumbine, Richard

    2012-01-01

    This article outlines an exercise that assesses student knowledge of food-web and energy-flow concepts. Students work in teams and use manipulatives to build food-web models based on criteria assigned by the instructor. The models are then peer reviewed according to guidelines supplied by the instructor.

  15. 40 CFR 230.31 - Fish, crustaceans, mollusks, and other aquatic organisms in the food web.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 25 2014-07-01 2014-07-01 false Fish, crustaceans, mollusks, and other... § 230.31 Fish, crustaceans, mollusks, and other aquatic organisms in the food web. (a) Aquatic organisms in the food web include, but are not limited to, finfish, crustaceans, mollusks, insects,...

  16. 40 CFR 230.31 - Fish, crustaceans, mollusks, and other aquatic organisms in the food web.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 26 2013-07-01 2013-07-01 false Fish, crustaceans, mollusks, and other... § 230.31 Fish, crustaceans, mollusks, and other aquatic organisms in the food web. (a) Aquatic organisms in the food web include, but are not limited to, finfish, crustaceans, mollusks, insects,...

  17. 40 CFR 230.31 - Fish, crustaceans, mollusks, and other aquatic organisms in the food web.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 25 2011-07-01 2011-07-01 false Fish, crustaceans, mollusks, and other... § 230.31 Fish, crustaceans, mollusks, and other aquatic organisms in the food web. (a) Aquatic organisms in the food web include, but are not limited to, finfish, crustaceans, mollusks, insects,...

  18. 40 CFR 230.31 - Fish, crustaceans, mollusks, and other aquatic organisms in the food web.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 26 2012-07-01 2011-07-01 true Fish, crustaceans, mollusks, and other... § 230.31 Fish, crustaceans, mollusks, and other aquatic organisms in the food web. (a) Aquatic organisms in the food web include, but are not limited to, finfish, crustaceans, mollusks, insects,...

  19. Climate change impacts on global food security.

    PubMed

    Wheeler, Tim; von Braun, Joachim

    2013-08-02

    Climate change could potentially interrupt progress toward a world without hunger. A robust and coherent global pattern is discernible of the impacts of climate change on crop productivity that could have consequences for food availability. The stability of whole food systems may be at risk under climate change because of short-term variability in supply. However, the potential impact is less clear at regional scales, but it is likely that climate variability and change will exacerbate food insecurity in areas currently vulnerable to hunger and undernutrition. Likewise, it can be anticipated that food access and utilization will be affected indirectly via collateral effects on household and individual incomes, and food utilization could be impaired by loss of access to drinking water and damage to health. The evidence supports the need for considerable investment in adaptation and mitigation actions toward a "climate-smart food system" that is more resilient to climate change influences on food security.

  20. Food webs: a ladder for picking strawberries or a practical tool for practical problems?

    PubMed

    Memmott, Jane

    2009-06-27

    While food webs have provided a rich vein of research material over the last 50 years, they have largely been the subject matter of the pure ecologist working in natural habitats. While there are some notable exceptions to this trend, there are, as I explain in this paper, many applied questions that could be answered using a food web approach. The paper is divided into two halves. The first half provides a brief review of six areas where food webs have begun to be used as an applied tool: restoration ecology, alien species, biological control, conservation ecology, habitat management and global warming. The second half outlines five areas in which a food web approach could prove very rewarding: urban ecology, agroecology, habitat fragmentation, cross-habitat food webs and ecosystem services.

  1. Using Stable Isotope Mixing in a Great Lakes Coastal Tributary to Determine Food Web Linkages in Young Fishes

    EPA Science Inventory

    Our objectives were to determine whether we can detect a stable isotope gradient along the river-Great Lake hydrologic continuum in a coastal river and use it to identify changes across this gradient in the food web supporting young-of-year (YOY) and juvenile fish production. We ...

  2. Change Management Meets Web 2.0

    ERIC Educational Resources Information Center

    Gale, Doug

    2008-01-01

    Web 2.0 is the term used to describe a group of web-based creativity, information-sharing, and collaboration tools including wikis, blogs, social networks, and folksonomies. The common thread in all of these tools is twofold: They enable collaboration and information sharing, and their impact on higher education has been dramatic. A recent study…

  3. The use of DNA barcodes in food web construction-terrestrial and aquatic ecologists unite!

    PubMed

    Roslin, Tomas; Majaneva, Sanna

    2016-09-01

    By depicting who eats whom, food webs offer descriptions of how groupings in nature (typically species or populations) are linked to each other. For asking questions on how food webs are built and work, we need descriptions of food webs at different levels of resolution. DNA techniques provide opportunities for highly resolved webs. In this paper, we offer an exposé of how DNA-based techniques, and DNA barcodes in particular, have recently been used to construct food web structure in both terrestrial and aquatic systems. We highlight how such techniques can be applied to simultaneously improve the taxonomic resolution of the nodes of the web (i.e., the species), and the links between them (i.e., who eats whom). We end by proposing how DNA barcodes and DNA information may allow new approaches to the construction of larger interaction webs, and overcome some hurdles to achieving adequate sample size. Most importantly, we propose that the joint adoption and development of these techniques may serve to unite approaches to food web studies in aquatic and terrestrial systems-revealing the extent to which food webs in these environments are structured similarly to or differently from each other, and how they are linked by dispersal.

  4. Parasites as prey in aquatic food webs: implications for predator infection and parasite transmission

    USGS Publications Warehouse

    Thieltges, David W.; Amundsen, Per-Arne; Hechinger, Ryan F.; Johnson, Pieter T.J.; Lafferty, Levin D.; Mouritsen, Kim N.; Preston, Daniel L.; Reise, Karsten; Zander, C. Dieter; Poulin, Robert

    2013-01-01

    While the recent inclusion of parasites into food-web studies has highlighted the role of parasites as consumers, there is accumulating evidence that parasites can also serve as prey for predators. Here we investigated empirical patterns of predation on parasites and their relationships with parasite transmission in eight topological food webs representing marine and freshwater ecosystems. Within each food web, we examined links in the typical predator–prey sub web as well as the predator–parasite sub web, i.e. the quadrant of the food web indicating which predators eat parasites. Most predator– parasite links represented ‘concomitant predation’ (consumption and death of a parasite along with the prey/host; 58–72%), followed by ‘trophic transmission’ (predator feeds on infected prey and becomes infected; 8–32%) and predation on free-living parasite life-cycle stages (4–30%). Parasite life-cycle stages had, on average, between 4.2 and 14.2 predators. Among the food webs, as predator richness increased, the number of links exploited by trophically transmitted parasites increased at about the same rate as did the number of links where these stages serve as prey. On the whole, our analyses suggest that predation on parasites has important consequences for both predators and parasites, and food web structure. Because our analysis is solely based on topological webs, determining the strength of these interactions is a promising avenue for future research.

  5. Assessing the trophic position and ecological role of squids in marine ecosystems by means of food-web models

    NASA Astrophysics Data System (ADS)

    Coll, Marta; Navarro, Joan; Olson, Robert J.; Christensen, Villy

    2013-10-01

    We synthesized available information from ecological models at local and regional scales to obtain a global picture of the trophic position and ecological role of squids in marine ecosystems. First, static food-web models were used to analyze basic ecological parameters and indicators of squids: biomass, production, consumption, trophic level, omnivory index, predation mortality diet, and the ecological role. In addition, we developed various dynamic temporal simulations using two food-web models that included squids in their parameterization, and we investigated potential impacts of fishing pressure and environmental conditions for squid populations and, consequently, for marine food webs. Our results showed that squids occupy a large range of trophic levels in marine food webs and show a large trophic width, reflecting the versatility in their feeding behaviors and dietary habits. Models illustrated that squids are abundant organisms in marine ecosystems, and have high growth and consumption rates, but these parameters are highly variable because squids are adapted to a large variety of environmental conditions. Results also show that squids can have a large trophic impact on other elements of the food web, and top-down control from squids to their prey can be high. In addition, some squid species are important prey of apical predators and may be keystone species in marine food webs. In fact, we found strong interrelationships between neritic squids and the populations of their prey and predators in coastal and shelf areas, while the role of squids in open ocean and upwelling ecosystems appeared more constrained to a bottom-up impact on their predators. Therefore, large removals of squids will likely have large-scale effects on marine ecosystems. In addition, simulations confirm that squids are able to benefit from a general increase in fishing pressure, mainly due to predation release, and quickly respond to changes triggered by the environment. Squids may thus

  6. Food Web Architecture and Basal Resources Interact to Determine Biomass and Stoichiometric Cascades along a Benthic Food Web

    PubMed Central

    Guariento, Rafael D.; Carneiro, Luciana S.; Caliman, Adriano; Leal, João J. F.; Bozelli, Reinaldo L.; Esteves, Francisco A.

    2011-01-01

    Understanding the effects of predators and resources on primary producers has been a major focus of interest in ecology. Within this context, the trophic cascade concept especially concerning the pelagic zone of lakes has been the focus of the majority of these studies. However, littoral food webs could be especially interesting because base trophic levels may be strongly regulated by consumers and prone to be light limited. In this study, the availability of nutrients and light and the presence of an omnivorous fish (Hyphessobrycon bifasciatus) were manipulated in enclosures placed in a humic coastal lagoon (Cabiúnas Lagoon, Macaé – RJ) to evaluate the individual and interactive effects of resource availability (nutrients and light) and food web configuration on the biomass and stoichiometry of periphyton and benthic grazers. Our findings suggest that light and nutrients interact to determine periphyton biomass and stoichiometry, which propagates to the consumer level. We observed a positive effect of the availability of nutrients on periphytic biomass and grazers' biomass, as well as a reduction of periphytic C∶N∶P ratios and an increase of grazers' N and P content. Low light availability constrained the propagation of nutrient effects on periphyton biomass and induced higher periphytic C∶N∶P ratios. The effects of fish presence strongly interacted with resource availability. In general, a positive effect of fish presence was observed for the total biomass of periphyton and grazer's biomass, especially with high resource availability, but the opposite was found for periphytic autotrophic biomass. Fish also had a significant effect on periphyton stoichiometry, but no effect was observed on grazers' stoichiometric ratios. In summary, we observed that the indirect effect of fish predation on periphyton biomass might be dependent on multiple resources and periphyton nutrient stoichiometric variation can affect consumers' stoichiometry. PMID:21789234

  7. Experimentally reducing species abundance indirectly affects food web structure and robustness.

    PubMed

    Barbosa, Milton; Fernandes, G Wilson; Lewis, Owen T; Morris, Rebecca J

    2017-03-01

    Studies on the robustness of ecological communities suggest that the loss or reduction in abundance of individual species can lead to secondary and cascading extinctions. However, most such studies have been simulation-based analyses of the effect of primary extinction on food web structure. In a field experiment we tested the direct and indirect effects of reducing the abundance of a common species, focusing on the diverse and self-contained assemblage of arthropods associated with an abundant Brazilian shrub, Baccharis dracunculifolia D.C. (Asteraceae). Over a 5-month period we experimentally reduced the abundance of Baccharopelma dracunculifoliae (Sternorrhyncha: Psyllidae), the commonest galling species associated with B. dracunculifolia, in 15 replicate plots paired with 15 control plots. We investigated direct effects of the manipulation on parasitoids attacking B. dracunculifoliae, as well as indirect effects (mediated via a third species or through the environment) on 10 other galler species and 50 associated parasitoid species. The experimental manipulation significantly increased parasitism on B. dracunculifoliae in the treatment plots, but did not significantly alter either the species richness or abundance of other galler species. Compared to control plots, food webs in manipulated plots had significantly lower values of weighted connectance, interaction evenness and robustness (measured as simulated tolerance to secondary extinction), even when B. dracunculifoliae was excluded from calculations. Parasitoid species were almost entirely specialized to individual galler species, so the observed effects of the manipulation on food web structure could not have propagated via the documented trophic links. Instead, they must have spread either through trophic links not included in the webs (e.g. shared predators) or non-trophically (e.g. through changes in habitat availability). Our results highlight that the inclusion of both trophic and non

  8. Watershed and Lake Influences on the Energetic Base of Coastal Wetland Food Webs across the Great Lakes Basin

    EPA Science Inventory

    This manuscript examines the responses of Great Lakes coastal wetland food webs to nutrient enrichment and identifies three classes of systems whose food webs respond differently. Or is that differentially? Anyway, coastal wetlands with relatively long hydraulic residence times ...

  9. Trophic levels and trophic tangles: the prevalence of omnivory in real food webs.

    PubMed

    Thompson, Ross M; Hemberg, Martin; Starzomski, Brian M; Shurin, Jonathan B

    2007-03-01

    The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top-down control within food webs, but it has been criticized for ignoring omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4%) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic-level-based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.

  10. Climate Change and Global Food Security: Food Access, Utilization, and the US Food System

    NASA Astrophysics Data System (ADS)

    Brown, M. E.; Antle, J. M.; Backlund, P. W.; Carr, E. R.; Easterling, W. E.; Walsh, M.; Ammann, C. M.; Attavanich, W.; Barrett, C. B.; Bellemare, M. F.; Dancheck, V.; Funk, C.; Grace, K.; Ingram, J. S. I.; Jiang, H.; Maletta, H.; Mata, T.; Murray, A.; Ngugi, M.; Ojima, D. S.; O'Neill, B. C.; Tebaldi, C.

    2015-12-01

    This paper will summarize results from the USDA report entitled 'Climate change, Global Food Security and the U.S. Food system'. The report focuses on the impact of climate change on global food security, defined as "when all people at all times have physical, social, and economic access to sufficient, safe, and nutritious food to meet their dietary needs and food preferences for an active and healthy life". The assessment brought together authors and contributors from twenty federal, academic, nongovernmental, intergovernmental, and private organizations in four countries to identify climate change effects on food security through 2100, and analyze the U.S.'s likely connections with that world. This talk will describe how climate change will likely affect food access and food utilization, and summarize how the U.S. food system contributes to global food security, and will be affected by climate change.

  11. Arthropod food webs become increasingly lipid-limited at higher trophic levels.

    PubMed

    Wilder, Shawn M; Norris, Michael; Lee, Raymond W; Raubenheimer, David; Simpson, Stephen J

    2013-07-01

    Understanding why food chains are relatively short in length has been an area of research and debate for decades. We tested if progressive changes in the nutritional content of arthropods with trophic position limit the availability of a key nutrient, lipid, for carnivores. Arthropods at higher trophic levels had progressively less lipid and more protein in their bodies compared with arthropods at lower trophic levels. The nutrients present in arthropod bodies were directly related to the nutrients that predators extracted when feeding on those arthropods. As a consequence, nutrient assimilation shifted from lipid-biased to protein-biased as arthropods ascended trophic levels from herbivores to secondary carnivores. Successive changes in the nutritional consequences of predation may ultimately set an upper limit on the number of trophic levels in arthropod communities. Further work is needed to examine the influence of lipid and other nutrients on food web traits in a range of ecosystems.

  12. Local adaptation to temperature conserves top-down control in a grassland food web.

    PubMed

    Barton, Brandon T

    2011-10-22

    A fundamental limitation in many climate change experiments is that tests represent relatively short-term 'shock' experiments and so do not incorporate the phenotypic plasticity or evolutionary change that may occur during the gradual process of climate change. However, capturing this aspect of climate change effects in an experimental design is a difficult challenge that few studies have accomplished. I examined the effect of temperature and predator climate history in food webs composed of herbaceous plants, generalist grasshopper herbivores and spider predators across a natural 4.8°C temperature gradient spanning 500 km in northeastern USA. In these grasslands, the effects of rising temperatures on the plant community are indirect and arise via altered predator-herbivore interactions. Experimental warming had no direct effect on grasshoppers, but reduced predation risk effects by causing spiders from all study sites to seek thermal refuge lower in the plant canopy. However, spider thermal tolerance corresponded to spider origin such that spiders from warmer study sites tolerated higher temperatures than spiders from cooler study sites. As a consequence, the magnitude of the indirect effect of spiders on plants did not differ along the temperature gradient, although a reciprocal transplant experiment revealed significantly different effects of spider origin on the magnitude of top-down control. These results suggest that variation in predator response to warming may maintain species interactions and associated food web processes when faced with long term, chronic climate warming.

  13. Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web

    PubMed Central

    Décima, Moira; Landry, Michael R.; Stukel, Michael R.; Lopez-Lopez, Lucia; Krause, Jeffrey W.

    2016-01-01

    We investigated standing stocks and grazing rates of mesozooplankton assemblages in the Costa Rica Dome (CRD), an open-ocean upwelling ecosystem in the eastern tropical Pacific. While phytoplankton biomass in the CRD is dominated by picophytoplankton (<2-µm cells) with especially high concentrations of Synechococcus spp., we found high mesozooplankton biomass (∼5 g dry weight m−2) and grazing impact (12–50% integrated water column chlorophyll a), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll a and mesozooplankton biomass, variability in herbivory was substantial, with lower rates in the central dome region and higher rates in areas offset from the dome center. While grazing rates were unrelated to total phytoplankton, correlations with cyanobacteria (negative) and biogenic SiO2 production (positive) suggest that partitioning of primary production among phytoplankton sizes contributes to the variability observed in mesozooplankton metrics. We propose that advection of upwelled waters away from the dome center is accompanied by changes in mesozooplankton composition and grazing rates, reflecting small changes within the primary producers. Small changes within the phytoplankton community resulting in large changes in the mesozooplankton suggest that the variability in lower trophic level dynamics was effectively amplified through the food web. PMID:27275033

  14. Invasive plants have different effects on trophic structure of green and brown food webs in terrestrial ecosystems: a meta-analysis.

    PubMed

    McCary, Matthew A; Mores, Robin; Farfan, Monica A; Wise, David H

    2016-03-01

    Although invasive plants are a major source of terrestrial ecosystem degradation worldwide, it remains unclear which trophic levels above the base of the food web are most vulnerable to plant invasions. We performed a meta-analysis of 38 independent studies from 32 papers to examine how invasive plants alter major groupings of primary and secondary consumers in three globally distributed ecosystems: wetlands, woodlands and grasslands. Within each ecosystem we examined if green (grazing) food webs are more sensitive to plant invasions compared to brown (detrital) food webs. Invasive plants have strong negative effects on primary consumers (detritivores, bacterivores, fungivores, and/or herbivores) in woodlands and wetlands, which become less abundant in both green and brown food webs in woodlands and green webs in wetlands. Plant invasions increased abundances of secondary consumers (predators and/or parasitoids) only in woodland brown food webs and green webs in wetlands. Effects of invasive plants on grazing and detrital food webs clearly differed between ecosystems. Overall, invasive plants had the most pronounced effects on the trophic structure of wetlands and woodlands, but caused no detectable changes to grassland trophic structure.

  15. Inverse modeling of carbon and nitrogen flows in the pelagic food web of the northeast subarctic Pacific

    NASA Astrophysics Data System (ADS)

    Vézina, A. F.; Savenkoff, C.

    1999-11-01

    We use inverse analysis to model carbon and nitrogen flows in the upper ocean food web at Ocean Station Papa (OSP; 50°N, 145°W) for winter, spring, and late summer. The seasonal variability in basic physical, chemical, and biological characteristics is low, and the particulate carbon and nitrogen flux at 200 m is remarkably constant. Despite this apparent uniformity, the food web structure undergoes significant seasonal changes. The diversity of trophic pathways is higher during late summer than during the other two periods. The spring ecosystem is not in steady state and undergoes net phytoplankton growth and macronutrient consumption. The microbial loop is well developed only during late summer. Nevertheless, ammonium regeneration by the food web seems insufficient to meet demand by the primary producers. The difference may be due to recycling of dissolved organic nitrogen (urea+free amino acids), a process not represented in the model. The winter food web is the closest to steady state, with nitrate utilisation approximately in balance with export of particulate nitrogen. The inverse analysis suggests two main seasonally invariant features of the NE Pacific ecosystem. First, the major trophic pathway is always from picophytoplankton (0.2-5 μm) to microzooplankton (heterotrophic dinoflagellates and ciliates) to mesozooplankton. This supports the idea of a strong coupling between the microbial and metazoan food webs. Second, much of the primary production (and bacterial production in late summer) is not grazed and is recycled through the detrital pool. Both these features seem to arise from the requirement to conserve nitrogen as well as carbon in the food web. More complete measurements on the microzooplankton 20-200 μm in size, including the small metazoans like nauplii larvae, are required to improve the models presented here.

  16. Effects of anthropogenic nitrogen input on the aquatic food webs of river ecosystem in central Japan

    NASA Astrophysics Data System (ADS)

    Ohte, N.; Togashi, H.; Tokuchi, N.; Yoshimura, M.; Kato, Y.; Ishikawa, N. F.; Osaka, K.; Kondo, M.; Tayasu, I.

    2014-12-01

    To evaluate the impact of the anthropogenic nitrogen input to the river ecosystem, we conducted the monitoring on nutrient status of river waters and food web structures of aquatic organisms. Especially, changes of sources and concentration of nitrate (NO3-) in river water were focused to evaluate the impact of anthropogenic nitrogen loadings from agricultural and residential areas. Stable nitrogen isotope ratio (δ15N) of aquatic organisms has also intensively been monitored not only to describe their food web structure, but also to detect the influences of extraneous nitrogen inputs. Field samplings an observation campaigns were conducted in the Arida river watershed located in central part of Japan at four different seasons from September 2011 to October 2012. Five observation points were set from headwaters to the point just above the brackish waters starts. Water samples for chemical analysis were taken at the observation points for each campaign. Organisms including leaf litters, benthic algae, aquatic insects, crustacean, and fishes were sampled at each point quantitatively. Results of the riverine survey utilizing 5 regular sampling points showed that δ15N of nitrate (NO3-) increased from forested upstream (˜2 ‰) to the downstream (˜7 ‰) due to the sewage loads and fertilizer effluents from agricultural area. Correspondingly the δ15N of benthic algae and aquatic insects increased toward the downstream. This indicates that primary producers of each reach strongly relied on the local N sources and it was utilized effectively in their food web. Simulation using a GIS based mixing model considering the spatial distributions of human population density and fertilizer effluents revealed that strongest impacts of N inputs was originated from organic fertilizers applied to orchards in the middle to lower parts of catchment. Differences in δ15N between primary producers and predators were 6-7 ‰ similarly at all sampling points. Food web structural

  17. Stable isotope analysis of a newly established macrofaunal food web 1.5 years after the Hebei Spirit oil spill.

    PubMed

    Han, Eunah; Park, Hyun Je; Bergamino, Leandro; Choi, Kwang-Sik; Choy, Eun Jung; Yu, Ok Hwan; Lee, Tae Won; Park, Heung-Sik; Shim, Won Joon; Kang, Chang-Keun

    2015-01-15

    We examined trophic relationships in a newly established community 1.5 years after the Hebei Spirit oil spill on the west coast of Korea. Carbon and nitrogen stable isotope ratios in consumers and their potential food sources were compared between the oil-spill site and reference site, located 13.5 km from the oil-spill spot. The isotopic mixing model and a novel circular statistics rejected the influx of petrogenic carbon into the community and identified spatial consistencies such as the high contributions of microphytobenthos, food-chain length, and the isotopic niche of each feeding guild between sites. We suggested that high level of trophic plasticity and the prevalence of omnivory of consumers may promote the robustness of food web against the oil contamination. Furthermore, we highlighted the need of holistic approaches including different functional groups to quantify changes in the food web structure and assess the influence of different perturbations including oil spill.

  18. Trophic groups and modules: two levels of group detection in food webs

    PubMed Central

    Gauzens, Benoit; Thébault, Elisa; Lacroix, Gérard; Legendre, Stéphane

    2015-01-01

    Within food webs, species can be partitioned into groups according to various criteria. Two notions have received particular attention: trophic groups (TGs), which have been used for decades in the ecological literature, and more recently, modules. The relationship between these two group concepts remains unknown in empirical food webs. While recent developments in network theory have led to efficient methods for detecting modules in food webs, the determination of TGs (groups of species that are functionally similar) is largely based on subjective expert knowledge. We develop a novel algorithm for TG detection. We apply this method to empirical food webs and show that aggregation into TGs allows for the simplification of food webs while preserving their information content. Furthermore, we reveal a two-level hierarchical structure where modules partition food webs into large bottom–top trophic pathways, whereas TGs further partition these pathways into groups of species with similar trophic connections. This provides new perspectives for the study of dynamical and functional consequences of food-web structure, bridging topological and dynamical analysis. TGs have a clear ecological meaning and are found to provide a trade-off between network complexity and information loss. PMID:25878127

  19. Trophic groups and modules: two levels of group detection in food webs.

    PubMed

    Gauzens, Benoit; Thébault, Elisa; Lacroix, Gérard; Legendre, Stéphane

    2015-05-06

    Within food webs, species can be partitioned into groups according to various criteria. Two notions have received particular attention: trophic groups (TGs), which have been used for decades in the ecological literature, and more recently, modules. The relationship between these two group concepts remains unknown in empirical food webs. While recent developments in network theory have led to efficient methods for detecting modules in food webs, the determination of TGs (groups of species that are functionally similar) is largely based on subjective expert knowledge. We develop a novel algorithm for TG detection. We apply this method to empirical food webs and show that aggregation into TGs allows for the simplification of food webs while preserving their information content. Furthermore, we reveal a two-level hierarchical structure where modules partition food webs into large bottom-top trophic pathways, whereas TGs further partition these pathways into groups of species with similar trophic connections. This provides new perspectives for the study of dynamical and functional consequences of food-web structure, bridging topological and dynamical analysis. TGs have a clear ecological meaning and are found to provide a trade-off between network complexity and information loss.

  20. Parameterizations of truncated food web models from the perspective of an end-to-end model approach

    NASA Astrophysics Data System (ADS)

    Fennel, Wolfgang

    2009-02-01

    Modeling of marine ecosystems is broadly divided into two branches: biogeochemical processes and fish production. The biogeochemical models see the fish only implicitly by mortality rates, while fish production models see the lower food web basically through prescribed food, e.g., copepod biomass. The skill assessment of ecological models, which are usually truncated biogeochemical models, also involves the question of how the effects of the missing higher food web are parameterized. This paper contributes to the goal of bridging biogeochemical models and fish-production models by employing a recently developed coupled NPZDF-model, Fennel [Fennel, W., 2007. Towards bridging biogeochemical and fish production models. Journal of Marine Systems, doi:10.1016/j.jmarsys.2007.06.008]. Here we study parameterizations of truncated NPZD-models from the viewpoint of a complete model. The effects of the higher food web on the cycling of the state variables in a truncated NPZD-model cannot be unambiguously imitated. For example, one can mimic effects of fishery by export fluxes of one of the state variables. It is shown that the mass fluxes between the lower and upper part of the full model food web are significantly smaller than the fluxes within the NPZD-model. However, over longer time scales, relatively small changes can accumulate and eventually become important.

  1. Nutrient enrichment reduces constraints on material flows in a detritus-based food web.

    PubMed

    Cross, Wyatt F; Wallace, J Bruce; Rosemond, Amy D

    2007-10-01

    Most aquatic and terrestrial ecosystems are experiencing increased nutrient availability, which is affecting their structure and function. By altering community composition and productivity of consumers, enrichment can indirectly cause changes in the pathways and magnitude of material flows in food webs. These changes, in turn, have major consequences for material storage and cycling in the ecosystem. Understanding mechanisms and predicting consequences of nutrient-induced changes in material flows requires a quantitative food web approach that combines information on consumer energetics and consumer-resource stoichiometry. We examined effects of a whole-system experimental nutrient enrichment on the trophic basis of production and the magnitude and pathways of carbon (C), nitrogen (N), and phosphorus (P) flows in a detritus-based stream food web. We compared the response of the treated stream to an adjacent reference stream throughout the study. Dietary composition and elemental flows varied considerably among invertebrate functional feeding groups. During nutrient enrichment, increased flows of leaf litter and amorphous detritus to shredders and gatherers accounted for most of the altered flows of C from basal resources to consumers. Nutrient enrichment had little effect on patterns of material flows but had large positive effects on the magnitude of C, N, and P flows to consumers (mean increase of 97% for all elements). Nutrient-specific food webs revealed similar flows of N and P to multiple functional groups despite an order of magnitude difference among groups in consumption of C. Secondary production was more strongly related to consumption of nutrients than C, and increased material flows were positively related to the degree of consumer-resource C:P and C:N imbalances. Nutrient enrichment resulted in an increased proportion of detrital C inputs consumed by primary consumers (from -15% to 35%) and a decreased proportion of invertebrate prey consumed by

  2. Invasive crayfish as vectors of mercury in freshwater food webs of the Pacific Northwest

    USGS Publications Warehouse

    Johnson, Branden L.; Willacker, James J.; Eagles-Smith, Collin A.; Pearl, Christopher A.; Adams, Michael J.

    2014-01-01

    Invasive species are important drivers of environmental change in aquatic ecosystems and can alter habitat characteristics, community composition, and ecosystem energetics. Such changes have important implications for many ecosystem processes, including the bioaccumulation and biomagnification of contaminants through food webs. Mercury concentrations were measured in 2 nonnative and 1 native crayfish species from western Oregon (USA). Nonnative red swamp crayfish had mercury concentrations similar to those in native signal crayfish (0.29 ± 0.05 µg/g dry wt and 0.36 ± 0.06 µg/g dry wt, respectively), whereas the nonnative ringed crayfish had lower mercury concentrations (0.10 ± 0.02 µg/g dry wt) than either of the other species. The mean energy content of muscle was similar between the native signal crayfish and nonnative ringed crayfish but was significantly higher in the nonnative red swamp crayfish. Across species, mercury concentrations were negatively correlated with energy density. Such energetic differences could exacerbate changes in mercury transfer through trophic pathways of food webs, especially via alterations to the growth dynamics of consumers. Thus, it is important to consider the role of energy content in determining effective mercury exposure even when mercury concentrations on a per-unit mass basis do not differ between species.

  3. Food webs in relation to variation in the environment and species assemblage: a multivariate approach.

    PubMed

    Schriever, Tiffany A

    2015-01-01

    The abiotic environment has strong influences on the growth, survival, behavior, and ecology of aquatic organisms. Biotic interactions and species life histories interact with abiotic factors to structure the food web. One measure of food-web structure is food-chain length. Several hypotheses predict a linear relationship between one environmental variable (e.g., disturbance or ecosystem size) and food-chain length. However, many abiotic and biotic variables interact in diverse ways to structure a community, and may affect other measures of food web structure besides food-chain length. This study took a multivariate approach to test the influence of several important environmental variables on four food-web characteristics measured in nine ponds along a hydroperiod gradient over two years. This approach allowed for testing the ecosystem size and dynamic constraints hypotheses while in context of other possibly interacting environmental variables. The relationship between amphibian and invertebrate communities and pond habitat variables was assessed to understand the underlying food-web structure. Hydroperiod and pond area had a strong influence on amphibian and invertebrate communities, trophic diversity and δ15N range. The range in δ13C values responded strongly to dissolved oxygen. Food-chain length responded to multiple environmental variables. Invertebrate and amphibian communities were structured by pond hydroperiod which in turn influenced the trophic diversity of the food web. The results of this study suggest food-chain length is influenced by environmental variation and species assemblage and that a multivariate approach may allow us to better understand the dynamics within and across aquatic food webs.

  4. Linking food web functioning and habitat diversity for an ecosystem based management: a Mediterranean lagoon case-study.

    PubMed

    Brigolin, D; Facca, C; Franco, A; Franzoi, P; Pastres, R; Sfriso, A; Sigovini, M; Soldatini, C; Tagliapietra, D; Torricelli, P; Zucchetta, M; Pranovi, F

    2014-06-01

    We propose a modelling approach relating the functioning of a transitional ecosystem with the spatial extension of its habitats. A test case is presented for the lagoon of Venice, discussing the results in the context of the application of current EU directives. The effects on food web functioning due to changes related to manageable and unmanageable drivers were investigated. The modelling procedure involved the use of steady-state food web models and network analysis, respectively applied to estimate the fluxes of energy associated with trophic interactions, and to compute indices of food web functioning. On the long term (hundred years) temporal scale, the model indicated that the expected loss of salt marshes will produce further changes at the system level, with a lagoon showing a decrease in the energy processing efficiency. On the short term scale, simulation results indicated that fishery management accompanied by seagrass restoration measures would produce a slight transition towards a more healthy system, with higher energy cycling, and maintaining a good balance between processing efficiency and resilience. Scenarios presented suggest that the effectiveness of short term management strategies can be better evaluated when contextualized in the long term trends of evolution of a system. We also remark the need for further studying the relationship between habitat diversity and indicators of food web functioning.

  5. Multiple predator effects in an intertidal food web.

    PubMed

    Van Son, Thijs Christiaan; Thiel, Martin

    2006-01-01

    1. We examined the effects of multiple predators from an intertidal boulder food web to test whether and how three different predator species affected the survival of a small amphipod species. 2. Predators were chosen because they differ in their foraging mode, two feeding at the bottom and in benthic refuges (nemertean and shrimp) and one in the water-column (juveniles of a fish). 3. Mortality of amphipods was not affected by nemerteans, but was high in the presence of shrimp or fish. Highest mortalities were observed in predator-combinations that contained both shrimp and fish. Amphipods responded to shrimp by escaping into the water column, while they avoided fish by remaining in the refuge. We conclude that predator-specific defence causes conflicts for prey when both shrimp and fish are present. 4. Comparing observed effects of multiple predators with expected effects revealed risk enhancement for the shrimp + fish combination. A comparison of different predictive models revealed that the multiplicative model was most appropriate, although additive models may work well under certain conditions. 5. Based on known consumption-ranges of the predators used, we conclude that nemerteans were saturated with prey while fish were far from their saturation point. A predator's functional response curve (prey consumption in relation to prey abundance) determines its impact on prey populations. This knowledge appears essential in order to predict whether prey organisms face risk enhancement, risk reduction or additive effects of multiple predators.

  6. Dispersed oil disrupts microbial pathways in pelagic food webs.

    PubMed

    Ortmann, Alice C; Anders, Jennifer; Shelton, Naomi; Gong, Limin; Moss, Anthony G; Condon, Robert H

    2012-01-01

    Most of the studies of microbial processes in response to the Deepwater Horizon oil spill focused on the deep water plume, and not on the surface communities. The effects of the crude oil and the application of dispersants on the coastal microbial food web in the northern Gulf of Mexico have not been well characterized even though these regions support much of the fisheries production in the Gulf. A mesocosm experiment was carried out to determine how the microbial community off the coast of Alabama may have responded to the influx of surface oil and dispersants. While the addition of glucose or oil alone resulted in an increase in the biomass of ciliates, suggesting transfer of carbon to higher trophic levels was likely; a different effect was seen in the presence of dispersant. The addition of dispersant or dispersed oil resulted in an increase in the biomass of heterotrophic prokaryotes, but a significant inhibition of ciliates, suggesting a reduction in grazing and decrease in transfer of carbon to higher trophic levels. Similar patterns were observed in two separate experiments with different starting nutrient regimes and microbial communities suggesting that the addition of dispersant and dispersed oil to the northern Gulf of Mexico waters in 2010 may have reduced the flow of carbon to higher trophic levels, leading to a decrease in the production of zooplankton and fish on the Alabama shelf.

  7. Transfer of heavy metals through terrestrial food webs: a review.

    PubMed

    Gall, Jillian E; Boyd, Robert S; Rajakaruna, Nishanta

    2015-04-01

    Heavy metals are released into the environment by both anthropogenic and natural sources. Highly reactive and often toxic at low concentrations, they may enter soils and groundwater, bioaccumulate in food webs, and adversely affect biota. Heavy metals also may remain in the environment for years, posing long-term risks to life well after point sources of heavy metal pollution have been removed. In this review, we compile studies of the community-level effects of heavy metal pollution, including heavy metal transfer from soils to plants, microbes, invertebrates, and to both small and large mammals (including humans). Many factors contribute to heavy metal accumulation in animals including behavior, physiology, and diet. Biotic effects of heavy metals are often quite different for essential and non-essential heavy metals, and vary depending on the specific metal involved. They also differ for adapted organisms, including metallophyte plants and heavy metal-tolerant insects, which occur in naturally high-metal habitats (such as serpentine soils) and have adaptations that allow them to tolerate exposure to relatively high concentrations of some heavy metals. Some metallophyte plants are hyperaccumulators of certain heavy metals and new technologies using them to clean metal-contaminated soil (phytoextraction) may offer economically attractive solutions to some metal pollution challenges. These new technologies provide incentive to catalog and protect the unique biodiversity of habitats that have naturally high levels of heavy metals.

  8. Analysis of governmental Web sites on food safety issues: a global perspective.

    PubMed

    Namkung, Young; Almanza, Barbara A

    2006-10-01

    Despite a growing concern over food safety issues, as well as a growing dependence on the Internet as a source of information, little research has been done to examine the presence and relevance of food safety-related information on Web sites. The study reported here conducted Web site analysis in order to examine the current operational status of governmental Web sites on food safety issues. The study also evaluated Web site usability, especially information dimensionalities such as utility, currency, and relevance of content, from the perspective of the English-speaking consumer. Results showed that out of 192 World Health Organization members, 111 countries operated governmental Web sites that provide information about food safety issues. Among 171 searchable Web sites from the 111 countries, 123 Web sites (71.9 percent) were accessible, and 81 of those 123 (65.9 percent) were available in English. The majority of Web sites offered search engine tools and related links for more information, but their availability and utility was limited. In terms of content, 69.9 percent of Web sites offered information on foodborne-disease outbreaks, compared with 31.5 percent that had travel- and health-related information.

  9. A unifying approach for food webs, phylogeny, social networks, and statistics

    PubMed Central

    Chiu, Grace S.; Westveld, Anton H.

    2011-01-01

    A food web consists of nodes, each consisting of one or more species. The role of each node as predator or prey determines the trophic relations that weave the web. Much effort in trophic food web research is given to understand the connectivity structure, or the nature and degree of dependence among nodes. Social network analysis (SNA) techniques—quantitative methods commonly used in the social sciences to understand network relational structure—have been used for this purpose, although postanalysis effort or biological theory is still required to determine what natural factors contribute to the feeding behavior. Thus, a conventional SNA alone provides limited insight into trophic structure. Here we show that by using novel statistical modeling methodologies to express network links as the random response of within- and internode characteristics (predictors), we gain a much deeper understanding of food web structure and its contributing factors through a unified statistical SNA. We do so for eight empirical food webs: Phylogeny is shown to have nontrivial influence on trophic relations in many webs, and for each web trophic clustering based on feeding activity and on feeding preference can differ substantially. These and other conclusions about network features are purely empirical, based entirely on observed network attributes while accounting for biological information built directly into the model. Thus, statistical SNA techniques, through statistical inference for feeding activity and preference, provide an alternative perspective of trophic clustering to yield comprehensive insight into food web structure. PMID:21896716

  10. Plankton food web and its seasonal dynamics in a large monsoonal estuary (Cochin backwaters, India)-significance of mesohaline region.

    PubMed

    Sooria, P M; Jyothibabu, R; Anjusha, A; Vineetha, G; Vinita, J; Lallu, K R; Paul, M; Jagadeesan, L

    2015-07-01

    The paper presents the ecology and dynamics of plankton food web in the Cochin backwaters (CBW), the largest monsoonal estuary along the west coast of India. The data source is a time series measurement carried out in the CBW during the Spring Intermonsoon (March-May) and the Southwest Monsoon (June-September). The plankton food web consisting of autotrophic/heterotrophic picoplankton, autotrophic/heterotrophic nanoplankton, microzooplankton, and mesozooplankton was quantified in relation to the seasonal hydrographical settings in the CBW. The study showed that significant changes in the abundance and dynamics of plankton food web components were governed mostly by the spatial and seasonal changes in hydrography rather than short-term changes induced by tide. During the Spring Intermonsoon, all plankton consumers in the CBW was higher than the Southwest Monsoon, and the trophic interaction was more effective in upstream where there was a close coupling between all prey components and their consumers. During the Southwest Monsoon, on the other hand, the trophic interaction was more effective downstream where the abundance of all plankton consumers was significantly higher than the upstream. Based on statistical analyses NMDS/SIMPROF and RDA, we demarcated the spatial difference/mismatch in the prey and consumer distribution in the CBW and showed that a more efficient plankton food web exists in the mesohaline regions during both seasons. This suggests that a noticeable spatial shift occurs seasonally in the active plankton food web zone in the CBW; it is upstream during the Spring Intermonsoon and downstream during the Southwest Monsoon.

  11. Impact of biodiversity loss on production in complex marine food webs mitigated by prey-release

    PubMed Central

    Fung, Tak; Farnsworth, Keith D.; Reid, David G.; Rossberg, Axel G.

    2015-01-01

    Public concern over biodiversity loss is often rationalized as a threat to ecosystem functioning, but biodiversity-ecosystem functioning (BEF) relations are hard to empirically quantify at large scales. We use a realistic marine food-web model, resolving species over five trophic levels, to study how total fish production changes with species richness. This complex model predicts that BEF relations, on average, follow simple Michaelis–Menten curves when species are randomly deleted. These are shaped mainly by release of fish from predation, rather than the release from competition expected from simpler communities. Ordering species deletions by decreasing body mass or trophic level, representing ‘fishing down the food web’, accentuates prey-release effects and results in unimodal relationships. In contrast, simultaneous unselective harvesting diminishes these effects and produces an almost linear BEF relation, with maximum multispecies fisheries yield at ≈40% of initial species richness. These findings have important implications for the valuation of marine biodiversity. PMID:25799523

  12. Interaction between top-down and bottom-up control in marine food webs.

    PubMed

    Lynam, Christopher Philip; Llope, Marcos; Möllmann, Christian; Helaouët, Pierre; Bayliss-Brown, Georgia Anne; Stenseth, Nils C

    2017-02-21

    Climate change and resource exploitation have been shown to modify the importance of bottom-up and top-down forces in ecosystems. However, the resulting pattern of trophic control in complex food webs is an emergent property of the system and thus unintuitive. We develop a statistical nondeterministic model, capable of modeling complex patterns of trophic control for the heavily impacted North Sea ecosystem. The model is driven solely by fishing mortality and climatic variables and based on time-series data covering >40 y for six plankton and eight fish groups along with one bird group (>20 y). Simulations show the outstanding importance of top-down exploitation pressure for the dynamics of fish populations. Whereas fishing effects on predators indirectly altered plankton abundance, bottom-up climatic processes dominate plankton dynamics. Importantly, we show planktivorous fish to have a central role in the North Sea food web initiating complex cascading effects across and between trophic levels. Our linked model integrates bottom-up and top-down effects and is able to simulate complex long-term changes in ecosystem components under a combination of stressor scenarios. Our results suggest that in marine ecosystems, pathways for bottom-up and top-down forces are not necessarily mutually exclusive and together can lead to the emergence of complex patterns of control.

  13. Interaction between top-down and bottom-up control in marine food webs

    PubMed Central

    Lynam, Christopher Philip; Llope, Marcos; Möllmann, Christian; Helaouët, Pierre; Bayliss-Brown, Georgia Anne; Stenseth, Nils C.

    2017-01-01

    Climate change and resource exploitation have been shown to modify the importance of bottom-up and top-down forces in ecosystems. However, the resulting pattern of trophic control in complex food webs is an emergent property of the system and thus unintuitive. We develop a statistical nondeterministic model, capable of modeling complex patterns of trophic control for the heavily impacted North Sea ecosystem. The model is driven solely by fishing mortality and climatic variables and based on time-series data covering >40 y for six plankton and eight fish groups along with one bird group (>20 y). Simulations show the outstanding importance of top-down exploitation pressure for the dynamics of fish populations. Whereas fishing effects on predators indirectly altered plankton abundance, bottom-up climatic processes dominate plankton dynamics. Importantly, we show planktivorous fish to have a central role in the North Sea food web initiating complex cascading effects across and between trophic levels. Our linked model integrates bottom-up and top-down effects and is able to simulate complex long-term changes in ecosystem components under a combination of stressor scenarios. Our results suggest that in marine ecosystems, pathways for bottom-up and top-down forces are not necessarily mutually exclusive and together can lead to the emergence of complex patterns of control. PMID:28167770

  14. Linking Food Webs and Biogeochemical Processes in Wetlands: Insights From Sulfur Isotopes

    NASA Astrophysics Data System (ADS)

    Stricker, C. A.; Guntenspergen, G. R.; Rye, R. O.

    2005-05-01

    To better understand the transfer of nutrients into prairie wetland food webs we have investigated the cycling of S (via S isotope systematics and geochemistry) in a prairie wetland landscape by characterizing sources (ground water, interstitial water, surface water) and processes in a small catchment comprised of four wetlands in eastern South Dakota. We focused on S to derive process information that is not generally available from carbon isotopes alone. The wetlands chosen for study spanned a considerable range in SO4 concentration (0.1-13.6 mM), which corresponded with landscape position. Ground water δ34SSO4 values remained relatively constant (mean = -13.2 per mil) through time. However, δ34SSO4 values of wetland surface waters ranged from -2.9 to -30.0 per mil (CDT) and were negatively correlated with SO4 concentrations (p<0.05). The isotopic variability of surface water SO4 resulted from mixing with re-oxidized sulfides associated with recently flushed wetland soils. The δ34S signatures of wetland primary (Gastropoda: Stagnicola elodes) and secondary (Odonata: Anax sp.) consumers were significantly related to surface water δ34SSO4 values (p<0.05) suggesting that food web components were responding to changes in the isotopic composition of the S source. Both primary and secondary consumer δ34S signatures differed between wetlands (ANOVA, p<0.05). These data illustrate the complexity of S cycling in prairie wetlands and the influence of wetland hydrologic and biogeochemical processes on prairie wetland food webs. Additionally, this work has demonstrated that sulfur isotopes can provide unique source and process information that cannot be derived from traditional carbon and nitrogen isotope studies.

  15. Evidence for the assimilation of ancient glacier organic carbon in a proglacial stream food web

    USGS Publications Warehouse

    Fellman, Jason; Hood, Eran; Raymond, Peter A.; Hudson, J.H.; Bozeman, Maura; Arimitsu, Mayumi L.

    2015-01-01

    We used natural abundance δ13C, δ15N, and Δ14C to compare trophic linkages between potential carbon sources (leaf litter, epilithic biofilm, and particulate organic matter) and consumers (aquatic macroinvertebrates and fish) in a nonglacial stream and two reaches of the heavily glaciated Herbert River. We tested the hypothesis that proglacial stream food webs are sustained by organic carbon released from glacial ecosystems. Carbon sources and consumers in the nonglacial stream had carbon isotope values that ranged from -30‰ to -25‰ for δ13C and from -14‰ to 53‰ for Δ14C reflecting a food web sustained mainly on contemporary primary production. In contrast, biofilm in the two glacial stream sites was highly Δ14C-depleted (-215‰ to 175‰) relative to the nonglacial stream consistent with the assimilation of ancient glacier organic carbon. IsoSource modeling showed that in upper Herbert River, macroinvertebrates (Δ14C = -171‰ to 22‰) and juvenile salmonids (Δ14C = −102‰ to 17‰) reflected a feeding history of both biofilm (~ 56%) and leaf litter (~ 40%). We estimate that in upper Herbert River on average 36% of the carbon incorporated into consumer biomass is derived from the glacier ecosystem. Thus, 14C-depleted glacial organic carbon was likely transferred to higher trophic levels through a feeding history of bacterial uptake of dissolved organic carbon and subsequent consumption of 14C-depleted biofilm by invertebrates and ultimately fish. Our findings show that the metazoan food web is sustained in part by glacial organic carbon such that future changes in glacial runoff could influence the stability and trophic structure of proglacial aquatic ecosystems.

  16. Reestablishing healthy food retail: changing the landscape of food deserts.

    PubMed

    Karpyn, Allison; Young, Candace; Weiss, Stephanie

    2012-02-01

    The term "food desert" was formally introduced into the lexicon in 1995 and has come to describe areas with limited access to affordable nutritious foods, particularly areas in lower-income neighborhoods. The definition has led to the development of national and regional maps that focus efforts on equity in food access. Recognition of food deserts also marks a strategic change in public health's approach to obesity prevention. Today's emphasis on prevention has shifted away from individual responsibility to the role of the environment in health promotion. A number of solutions are underway to address food deserts, including public–private financing programs, industry commitments, as well as local and regional efforts to put healthy food within reach. The promise of financing programs to facilitate development of healthy food markets in underserved communities is rooted in their potential to alleviate the grocery gap and address underlying environmental contributors to obesity and diet-related diseases, such as obesity and diabetes. As food desert mapping and related interventions expand, there remains a need for ongoing investigation of impacts and the mechanisms by which impacts are achieved.

  17. Applying linear programming to estimate fluxes in ecosystems or food webs: An example from the herpetological assemblage of the freshwater Everglades

    USGS Publications Warehouse

    Diffendorfer, James E.; Richards, Paul M.; Dalrymple, George H.; DeAngelis, Donald L.

    2001-01-01

    We present the application of Linear Programming for estimating biomass fluxes in ecosystem and food web models. We use the herpetological assemblage of the Everglades as an example. We developed food web structures for three common Everglades freshwater habitat types: marsh, prairie, and upland. We obtained a first estimate of the fluxes using field data, literature estimates, and professional judgment. Linear programming was used to obtain a consistent and better estimate of the set of fluxes, while maintaining mass balance and minimizing deviations from point estimates. The results support the view that the Everglades is a spatially heterogeneous system, with changing patterns of energy flux, species composition, and biomasses across the habitat types. We show that a food web/ecosystem perspective, combined with Linear Programming, is a robust method for describing food webs and ecosystems that requires minimal data, produces useful post-solution analyses, and generates hypotheses regarding the structure of energy flow in the system.

  18. Examining Long-Term Global Climate Change on the Web.

    ERIC Educational Resources Information Center

    Huntoon, Jacqueline E.; Ridky, Robert K.

    2002-01-01

    Describes a web-based, inquiry-oriented activity that enables students to examine long-term global climate change. Supports instruction in other topics such as population growth. (Contains 34 references.) (DDR)

  19. Non-random food-web assembly at habitat edges increases connectivity and functional redundancy.

    PubMed

    Peralta, Guadalupe; Frost, Carol M; Didham, Raphael K; Rand, Tatyana A; Tylianakis, Jason M

    2017-04-01

    Habitat fragmentation dramatically alters the spatial configuration of landscapes, with the creation of artificial edges affecting community structure and dynamics. Despite this, it is not known how the different food webs in adjacent habitats assemble at their boundaries. Here we demonstrate that the composition and structure of herbivore-parasitoid food webs across edges between native and plantation forests are not randomly assembled from those of the adjacent communities. Rather, elevated proportions of abundant, interaction-generalist parasitoid species at habitat edges allowed considerable interaction rewiring, which led to higher linkage density and less modular networks, with higher parasitoid functional redundancy. This was despite high overlap in host composition between edges and interiors. We also provide testable hypotheses for how food webs may assemble between habitats with lower species overlap. In an increasingly fragmented world, non-random assembly of food webs at edges may increasingly affect community dynamics at the landscape level.

  20. Energy and nutrient flows connecting coastal wetland food webs to land and lake

    EPA Science Inventory

    Both landscape character and hydrologic forces (principally, tributary discharge and seiches) can influence utilization of externally-derived energy and nutrients in coastal wetland food webs. We quantified the contribution of internal vs external energy and nutrients among wetla...

  1. Integrating Ecosystem Engineering and Food Web Ecology: Testing the Effect of Biogenic Reefs on the Food Web of a Soft-Bottom Intertidal Area.

    PubMed

    De Smet, Bart; Fournier, Jérôme; De Troch, Marleen; Vincx, Magda; Vanaverbeke, Jan

    2015-01-01

    The potential of ecosystem engineers to modify the structure and dynamics of food webs has recently been hypothesised from a conceptual point of view. Empirical data on the integration of ecosystem engineers and food webs is however largely lacking. This paper investigates the hypothesised link based on a field sampling approach of intertidal biogenic aggregations created by the ecosystem engineer Lanice conchilega (Polychaeta, Terebellidae). The aggregations are known to have a considerable impact on the physical and biogeochemical characteristics of their environment and subsequently on the abundance and biomass of primary food sources and the macrofaunal (i.e. the macro-, hyper- and epibenthos) community. Therefore, we hypothesise that L. conchilega aggregations affect the structure, stability and isotopic niche of the consumer assemblage of a soft-bottom intertidal food web. Primary food sources and the bentho-pelagic consumer assemblage of a L. conchilega aggregation and a control area were sampled on two soft-bottom intertidal areas along the French coast and analysed for their stable isotopes. Despite the structural impacts of the ecosystem engineer on the associated macrofaunal community, the presence of L. conchilega aggregations only has a minor effect on the food web structure of soft-bottom intertidal areas. The isotopic niche width of the consumer communities of the L. conchilega aggregations and control areas are highly similar, implying that consumer taxa do not shift their diet when feeding in a L. conchilega aggregation. Besides, species packing and hence trophic redundancy were not affected, pointing to an unaltered stability of the food web in the presence of L. conchilega.

  2. Integrating Ecosystem Engineering and Food Web Ecology: Testing the Effect of Biogenic Reefs on the Food Web of a Soft-Bottom Intertidal Area

    PubMed Central

    De Smet, Bart; Fournier, Jérôme; De Troch, Marleen; Vincx, Magda; Vanaverbeke, Jan

    2015-01-01

    The potential of ecosystem engineers to modify the structure and dynamics of food webs has recently been hypothesised from a conceptual point of view. Empirical data on the integration of ecosystem engineers and food webs is however largely lacking. This paper investigates the hypothesised link based on a field sampling approach of intertidal biogenic aggregations created by the ecosystem engineer Lanice conchilega (Polychaeta, Terebellidae). The aggregations are known to have a considerable impact on the physical and biogeochemical characteristics of their environment and subsequently on the abundance and biomass of primary food sources and the macrofaunal (i.e. the macro-, hyper- and epibenthos) community. Therefore, we hypothesise that L. conchilega aggregations affect the structure, stability and isotopic niche of the consumer assemblage of a soft-bottom intertidal food web. Primary food sources and the bentho-pelagic consumer assemblage of a L. conchilega aggregation and a control area were sampled on two soft-bottom intertidal areas along the French coast and analysed for their stable isotopes. Despite the structural impacts of the ecosystem engineer on the associated macrofaunal community, the presence of L. conchilega aggregations only has a minor effect on the food web structure of soft-bottom intertidal areas. The isotopic niche width of the consumer communities of the L. conchilega aggregations and control areas are highly similar, implying that consumer taxa do not shift their diet when feeding in a L. conchilega aggregation. Besides, species packing and hence trophic redundancy were not affected, pointing to an unaltered stability of the food web in the presence of L. conchilega. PMID:26496349

  3. Climate change and sustainable food production.

    PubMed

    Smith, Pete; Gregory, Peter J

    2013-02-01

    One of the greatest challenges we face in the twenty-first century is to sustainably feed nine to ten billion people by 2050 while at the same time reducing environmental impact (e.g. greenhouse gas (GHG) emissions, biodiversity loss, land use change and loss of ecosystem services). To this end, food security must be delivered. According to the United Nations definition, 'food security exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life'. At the same time as delivering food security, we must also reduce the environmental impact of food production. Future climate change will make an impact upon food production. On the other hand, agriculture contributes up to about 30% of the anthropogenic GHG emissions that drive climate change. The aim of this review is to outline some of the likely impacts of climate change on agriculture, the mitigation measures available within agriculture to reduce GHG emissions and outlines the very significant challenge of feeding nine to ten billion people sustainably under a future climate, with reduced emissions of GHG. Each challenge is in itself enormous, requiring solutions that co-deliver on all aspects. We conclude that the status quo is not an option, and tinkering with the current production systems is unlikely to deliver the food and ecosystems services we need in the future; radical changes in production and consumption are likely to be required over the coming decades.

  4. Eating from the same plate? Revisiting the role of labile carbon inputs in the soil food web.

    PubMed

    de Vries, Franciska T; Caruso, Tancredi

    2016-11-01

    An increasing number of empirical studies are challenging the central fundamentals on which the classical soil food web model is built. This model assumes that bacteria consume labile substrates twice as fast as fungi, and that mycorrhizal fungi do not decompose organic matter. Here, we build on emerging evidence that points to significant consumption of labile C by fungi, and to the ability of ectomycorrhizal fungi to decompose organic matter, to show that labile C constitutes a major and presently underrated source of C for the soil food web. We use a simple model describing the dynamics of a recalcitrant and a labile C pool and their consumption by fungi and bacteria to show that fungal and bacterial populations can coexist in a stable state with large inputs into the labile C pool and a high fungal use of labile C. We propose a new conceptual model for the bottom trophic level of the soil food web, with organic C consisting of a continuous pool rather than two or three distinct pools, and saprotrophic fungi using substantial amounts of labile C. Incorporation of these concepts will increase our understanding of soil food web dynamics and functioning under changing conditions.

  5. The importance of landscape and spatial structure for hymenopteran-based food webs in an agro-ecosystem.

    PubMed

    Fabian, Yvonne; Sandau, Nadine; Bruggisser, Odile T; Aebi, Alex; Kehrli, Patrik; Rohr, Rudolf P; Naisbit, Russell E; Bersier, Louis-Félix

    2013-11-01

    1. Understanding the environmental factors that structure biodiversity and food webs among communities is central to assess and mitigate the impact of landscape changes. 2. Wildflower strips are ecological compensation areas established in farmland to increase pollination services and biological control of crop pests and to conserve insect diversity. They are arranged in networks in order to favour high species richness and abundance of the fauna. 3. We describe results from experimental wildflower strips in a fragmented agricultural landscape, comparing the importance of landscape, of spatial arrangement and of vegetation on the diversity and abundance of trap-nesting bees, wasps and their enemies, and the structure of their food webs. 4. The proportion of forest cover close to the wildflower strips and the landscape heterogeneity stood out as the most influential landscape elements, resulting in a more complex trap-nest community with higher abundance and richness of hosts, and with more links between species in the food webs and a higher diversity of interactions. We disentangled the underlying mechanisms for variation in these quantitative food web metrics. 5. We conclude that in order to increase the diversity and abundance of pollinators and biological control agents and to favour a potentially stable community of cavity-nesting hymenoptera in wildflower strips, more investment is needed in the conservation and establishment of forest habitats within agro-ecosystems, as a reservoir of beneficial insect populations.

  6. Effects of Seasonal and Spatial Differences in Food Webs on Mercury Concentrations in Fish in the Everglades

    NASA Astrophysics Data System (ADS)

    Kendall, C.; Bemis, B. E.; Wankel, S. D.; Rawlik, P. S.; Lange, T.; Krabbenhoft, D. P.

    2002-05-01

    A clear understanding of the aquatic food web is essential for determining the entry points and subsequent biomagnification pathways of contaminants such as methyl-mercury (MeHg) in the Everglades. Anthropogenic changes in nutrients can significantly affect the entry points of MeHg by changing food web structure from one dominated by algal productivity to one dominated by macrophytes and associated microbial activity. These changes in the base of the food web can also influence the distribution of animals within the ecosystem, and subsequently the bioaccumulation of MeHg up the food chain. As part of several collaborations with local and other federal agencies, more than 7000 Everglades samples were collected in 1995-99, and analysed for d13C and d15N. Many organisms were also analysed for d34S, gut contents, total Hg, and MeHg. Carbon isotopes effectively distinguish between two main types of food webs: ones where algae is the dominant base of the food web, which are characteristic of relatively pristine marsh sites with long hydroperiods, and ones where macrophyte debris appears to be a significant source of nutrients, which are apparently characteristic of shorter hydroperiod sites, and nutrient-impacted marshes and canals. Many organisms show significant (5-12%) spatial and temporal differences in d13C and d15N values across the Everglades. These differences may reflect site and season-specific differences in the relative importance of algae vs. macrophyte debris to the food web. However, there is a lack of evidence that these sites otherwise differ in food chain length (as determined by d15N values). This conclusion is generally supported by gut contents and mercury data. Furthermore, there are no statistically significant differences between the Delta d15N (predator-algae) values at pristine marsh, nutrient-impacted marsh, or canal sites. The main conclusions from this preliminary comparison of gut contents, stable isotope, and Hg data are: (1) there is

  7. The bioenergetic consequences of invasive-induced food web disruption to Lake Ontario alewives

    USGS Publications Warehouse

    Stewart, Thomas J.; O'Gorman, Robert; Sprules, W. Gary; Lantry, B.F.

    2010-01-01

    Alewives Alosa pseudoharengus are the dominant prey fish in Lake Ontario, and their response to ecological change can alter the structure and function of the Lake Ontario food web. Using stochastic population-based bioenergetic models of Lake Ontario alewives for 1987–1991 and 2001–2005, we evaluated changes to alewife production, consumption, and associated bioenergetic ratios after invasive-induced food web disruption. After the disruption, mean biomass of alewives declined from 28.0 to 14.6 g/m2, production declined from 40.8 to 13.6 g·m−2·year−1, and consumption declined from 342.1 to 137.2 g·m−2·year−1, but bootstrapping of error sources suggested that the changes were not statistically significant. Population-based bioenergetic ratios of production to biomass (P/B ratio), total consumption to biomass (Q/B ratio), and production efficiency did not change. Pathways of energy flow measured as prey-group-specific Q/B ratios changed significantly between the two time periods for invasive predatory cladocerans (from 0.6 to 1.3), Mysis diluviana (from 0.4 to 2.5), and other prey (from 0.8 to 0.1), but the observed decline in the zooplankton Q/B ratio (from 10.6 to 5.5) was not significant. Gross production efficiency did not change; values ranged from 8% to 15%. Age-group mean gross conversion efficiency (GCE) declined with age; GCE ranged from 7.5% to 11.0% for yearlings, was approximately 5% for age-2 alewives, and was less than 2% for age-3 and older alewives. The GCE increased significantly between the time periods for yearling alewives. Our analyses support the hypothesis that after 2003, alewives could not sustain their growth while feeding on zooplankton closer to shore. Modeling of observed spatial variation in diet and alternative occupied temperatures demonstrates the potential for reducing consumption by alewives. Our results suggest that Lake Ontario alewives can exploit spatial heterogeneity in resource patches and thermal habitat to

  8. Food web topology and parasites in the pelagic zone of a subarctic lake

    USGS Publications Warehouse

    Amundsen, P.-A.; Lafferty, K.D.; Knudsen, R.; Primicerio, R.; Klemetsen, A.; Kuris, A.M.

    2009-01-01

    Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2. Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3. More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4. For trophically transmitted parasites, the number of parasite-host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5. The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. ?? 2009 British Ecological Society.

  9. Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling.

    PubMed

    Legagneux, P; Gauthier, G; Berteaux, D; Bêty, J; Cadieux, M C; Bilodeau, F; Bolduc, E; McKinnon, L; Tarroux, A; Therrien, J F; Morissette, L; Krebs, C J

    2012-07-01

    Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of

  10. Incorporation of plant carbon into the soil animal food web of an arable system.

    PubMed

    Albers, Derk; Schaefer, Matthias; Scheu, Stefan

    2006-01-01

    We used stable isotopes to examine the incorporation of plant carbon into the belowground food web of an agricultural system. Plots were established and planted with maize (Zea mays) in a rye field (Secale cereale) near Göttingen (northern Germany) in May 1999. In October 1999, April 2000, and October 2000, meso- and macrofauna and maize and rye litter were collected in each plot and analyzed for 13C and 15N content. 15N signatures suggested that the soil animal species analyzed span three trophic levels with the trophic position of species varying little in time. The species investigated formed a continuum from primary to secondary decomposers to predators. On average, predator species differed from primary and secondary decomposers by 3.9 sigma15N suggesting that they fed on a mixed diet of both decomposer groups. The combined analysis of 13C and 15N signatures allowed us to identify links between prey and consumer species. In October 1999, shortly after maize residues had been incorporated into the plots, maize-born carbon was present in each of the animal species investigated, including top predators. The incorporation of maize carbon into the belowground food web increased during the following 12 months but the concentration of maize-born carbon never exceeded 50% in any of the species. Furthermore, the ranks of the incorporation of maize-born carbon of the species changed little. The results suggest that the belowground food web relies heavily on carbon originating from plant residues from before the recent two growing seasons. In most species the amount of maize-born carbon increased continuously; however, in some species it decreased during winter, suggesting that these species switched to a diet based more on C3 plants during winter, or predominantly metabolized carbon incorporated during the last growing season. The study documents that the combined analysis of 13C and 15N signatures in soil invertebrate species, after replacement of C3 by C4 plants, is

  11. Climate-driven warming during spring destabilises a Daphnia population: a mechanistic food web approach.

    PubMed

    Wagner, Annekatrin; Benndorf, Jürgen

    2007-03-01

    Temperature-driven changes in interactions between populations are crucial to the estimation of the impact of global warming on aquatic food webs. We analysed inter-annual variability in two data sets from Bautzen reservoir, Germany. In a long-term data set (1981-1999) we examined the pelagic phenology of Daphnia galeata, a keystone species, the invertebrate predator Leptodora kindtii, phytoplankton and Secchi depth in relation to water temperature and the North Atlantic Oscillation index. In a short-term data set (1995-1998) we examined food web relations, particularly the consumption of D. galeata by young-of-the-year (YOY) percids and L. kindtii and rates of population change of D. galeata (abundance, recruitment pattern and non-consumptive mortality). The start of the clear-water stage (CWS) was correlated with winter temperatures. It started 5.8 days earlier per degree warming after warm winters (mean January-March temperature>or=2.5 degrees C) compared to cold winters (mean temperature<2.5 degrees C). However, the end of the CWS remained relatively constant. Predation by L. kindtii and YOY percids on D. galeata started distinctly earlier, i.e. by 13.0 and 6.5 days per degree warming, respectively, in years when the average May temperature was high (>or=14 degrees C) compared to years when it was low (<14 degrees C). Significant reductions of Daphnia abundance in midsummer occurred only in years in which the mean May temperature exceeded 14 degrees C. This temperature regime resulted in a match of over-exploitation of food resources by Daphnia during the CWS and strong predation by YOY percids and L. kindtii. Consumptive mortality increased at higher rates with a rise in temperature than net recruitment, resulting in lower Daphnia densities at the end of the CWS. Our data suggest that even low warming by 1.7 degrees C during a short, but critical seasonal period, resulting in the coincidence of two or more factors adversely affecting a keystone species, such

  12. Development of a multichemical food web model: application to PBDEs in Lake Ellasjoen, Bear Island, Norway.

    PubMed

    Gandhi, Nilima; Bhavsar, Satyendra P; Gewurtz, Sarah B; Diamond, Miriam L; Evenset, Anita; Christensen, Guttorm N; Gregor, Dennis

    2006-08-01

    A multichemical food web model has been developed to estimate the biomagnification of interconverting chemicals in aquatic food webs. We extended a fugacity-based food web model for single chemicals to account for reversible and irreversible biotransformation among a parent chemical and transformation products, by simultaneously solving mass balance equations of the chemicals using a matrix solution. The model can be applied to any number of chemicals and organisms or taxonomic groups in a food web. The model was illustratively applied to four PBDE congeners, BDE-47, -99, -100, and -153, in the food web of Lake Ellasjøen, Bear Island, Norway. In Ellasjøen arctic char (Salvelinus alpinus), the multichemical model estimated PBDE biotransformation from higher to lower brominated congeners and improved the correspondence between estimated and measured concentrations in comparison to estimates from the single-chemical food web model. The underestimation of BDE-47, even after considering bioformation due to biotransformation of the otherthree congeners, suggests its formation from additional biotransformation pathways not considered in this application. The model estimates approximate values for congener-specific biotransformation half-lives of 5.7,0.8,1.14, and 0.45 years for BDE-47, -99, -100, and -153, respectively, in large arctic char (S. alpinus) of Lake Ellasjøen.

  13. Dynamically Coupled Food-web and Hydrodynamic Modeling with ADH-CASM

    NASA Astrophysics Data System (ADS)

    Piercy, C.; Swannack, T. M.

    2012-12-01

    Oysters and freshwater mussels are "ecological engineers," modifying the local water quality by filtering zooplankton and other suspended particulate matter from the water column and flow hydraulics by impinging on the near-bed flow environment. The success of sessile, benthic invertebrates such as oysters depends on environmental factors including but not limited to temperature, salinity, and flow regime. Typically food-web and other types of ecological models use flow and water quality data as direct input without regard to the feedback between the ecosystem and the physical environment. The USACE-ERDC has developed a coupled hydrodynamic-ecological modeling approach that dynamically couples a 2-D hydrodynamic and constituent transport model, Adaptive Hydraulics (ADH), with a bioenergetics food-web model, the Comprehensive Aquatics Systems Model (CASM), which captures the dynamic feedback between aquatic ecological systems and the environment. We present modeling results from restored oyster reefs in the Great Wicomico River on the western shore of the Chesapeake Bay, which quantify ecosystem services such as the influence of the benthic ecosystem on water quality. Preliminary results indicate that while the influence of oyster reefs on bulk flow dynamics is limited due to the localized influence of oyster reefs, large reefs and the associated benthic ecosystem can create measurable changes in the concentrations of nitrogen, phosphorus, and carbon in the areas around reefs. We also present a sensitivity analysis to quantify the relative sensitivity of the coupled ADH-CASM model to both hydrodynamic and ecological parameter choice.

  14. Terrestrial support of lake food webs: Synthesis reveals controls over cross-ecosystem resource use.

    PubMed

    Tanentzap, Andrew J; Kielstra, Brian W; Wilkinson, Grace M; Berggren, Martin; Craig, Nicola; Del Giorgio, Paul A; Grey, Jonathan; Gunn, John M; Jones, Stuart E; Karlsson, Jan; Solomon, Christopher T; Pace, Michael L

    2017-03-01

    Widespread evidence that organic matter exported from terrestrial into aquatic ecosystems supports recipient food webs remains controversial. A pressing question is not only whether high terrestrial support is possible but also what the general conditions are under which it arises. We assemble the largest data set, to date, of the isotopic composition (δ(2)H, δ(13)C, and δ(15)N) of lake zooplankton and the resources at the base of their associated food webs. In total, our data set spans 559 observations across 147 lakes from the boreal to subtropics. By predicting terrestrial resource support from within-lake and catchment-level characteristics, we found that half of all consumer observations that is, the median were composed of at least 42% terrestrially derived material. In general, terrestrial support of zooplankton was greatest in lakes with large physical and hydrological connections to catchments that were rich in aboveground and belowground organic matter. However, some consumers responded less strongly to terrestrial resources where within-lake production was elevated. Our study shows that multiple mechanisms drive widespread cross-ecosystem support of aquatic consumers across Northern Hemisphere lakes and suggests that changes in terrestrial landscapes will influence ecosystem processes well beyond their boundaries.

  15. Incorporation of an invasive plant into a native insect herbivore food web

    PubMed Central

    Santos Pimenta, Lúcia P.; Lammers, Youri; Steenbergen, Peter J.; Flohil, Marco; Beveridge, Nils G.P.; van Duijn, Pieter T.; Meulblok, Marjolein M.; Sosef, Nils; van de Ven, Robin; Werring, Ralf; Beentjes, Kevin K.; Meijer, Kim; Vos, Rutger A.; Vrieling, Klaas; Gravendeel, Barbara; Choi, Young; Verpoorte, Robert; Smit, Chris; Beukeboom, Leo W.

    2016-01-01

    The integration of invasive species into native food webs represent multifarious dynamics of ecological and evolutionary processes. We document incorporation of Prunus serotina (black cherry) into native insect food webs. We find that P. serotina harbours a herbivore community less dense but more diverse than its native relative, P. padus (bird cherry), with similar proportions of specialists and generalists. While herbivory on P. padus remained stable over the past century, that on P. serotina gradually doubled. We show that P. serotina may have evolved changes in investment in cyanogenic glycosides compared with its native range. In the leaf beetle Gonioctena quinquepunctata, recently shifted from native Sorbus aucuparia to P. serotina, we find divergent host preferences on Sorbus- versus Prunus-derived populations, and weak host-specific differentiation among 380 individuals genotyped for 119 SNP loci. We conclude that evolutionary processes may generate a specialized herbivore community on an invasive plant, allowing prognoses of reduced invasiveness over time. On the basis of the results presented here, we would like to caution that manual control might have the adverse effect of a slowing down of processes of adaptation, and a delay in the decline of the invasive character of P. serotina. PMID:27190702

  16. An indicator-based evaluation of Black Sea food web dynamics during 1960-2000

    NASA Astrophysics Data System (ADS)

    Akoglu, Ekin; Salihoglu, Baris; Libralato, Simone; Oguz, Temel; Solidoro, Cosimo

    2014-06-01

    Four Ecopath mass-balance models were implemented for evaluating the structure and function of the Black Sea ecosystem using several ecological indicators during four distinctive periods (1960s, 1980-1987, 1988-1994 and 1995-2000). The results exemplify how the Black Sea ecosystem structure started to change after the 1960s as a result of a series of trophic transformations, i.e., shifts in the energy flow pathways through the food web. These transformations were initiated by anthropogenic factors, such as eutrophication and overfishing, that led to the transfer of large quantities of energy to the trophic dead-end species, which had no natural predators in the ecosystem, i.e., jellyfish whose biomass increased from 0.03 g C m- 2 in 1960-1969 to 0.933 g C m- 2 in 1988-1994. Concurrently, an alternative short pathway for energy transfer was formed that converted significant amounts of system production back to detritus. This decreased the transfer efficiency of energy flow from the primary producers to the higher trophic levels from 9% in the 1960s to 3% between 1980 and 1987. We conclude that the anchovy stock collapse and successful establishment of the alien comb-jelly Mnemiopsis in 1989 were rooted in the trophic interactions in the food web, all of which were exacerbated because of the long-term establishment of a combination of anthropogenic stressors.

  17. Predator richness has no effect in a diverse marine food web.

    PubMed

    O'Connor, Mary I; Bruno, John F

    2009-07-01

    1. In many ecosystems, predator abundance, composition and diversity vary naturally among seasons and habitats. In addition, predator assemblages are changing due to overharvesting, habitat destruction and species invasions. 2. Predator species composition and richness can influence prey community structure and these effects can cascade to influence plant abundance and composition. 3. To test the effects of predator presence, composition and species richness on prey abundance, species richness and composition, we conducted three experiments in a subtidal marine food web. Experimental food webs were drawn from species pools of 5-7 predator species, 19-52 prey species, benthic micro-algae and 5 macro-algae. 4. Predators reduced prey abundance in the mesocosm experiment, but this effect was diminished or absent in field experiments. Predator species differed in their effects on prey, but we found no effect of predator richness (via complementarity or selection) on any aspect of prey community structure. 5. The absence of a predator richness effect could be due to several factors including potentially opposing effects of individual predator species, intraguild predation, or greater importance of colonization relative to competition in structuring prey assemblages. Although predators can have strong top-down effects in this system, selection or resource-use complementarity among predators do not affect prey community structure.

  18. Terrestrial support of lake food webs: Synthesis reveals controls over cross-ecosystem resource use

    PubMed Central

    Tanentzap, Andrew J.; Kielstra, Brian W.; Wilkinson, Grace M.; Berggren, Martin; Craig, Nicola; del Giorgio, Paul A.; Grey, Jonathan; Gunn, John M.; Jones, Stuart E.; Karlsson, Jan; Solomon, Christopher T.; Pace, Michael L.

    2017-01-01

    Widespread evidence that organic matter exported from terrestrial into aquatic ecosystems supports recipient food webs remains controversial. A pressing question is not only whether high terrestrial support is possible but also what the general conditions are under which it arises. We assemble the largest data set, to date, of the isotopic composition (δ2H, δ13C, and δ15N) of lake zooplankton and the resources at the base of their associated food webs. In total, our data set spans 559 observations across 147 lakes from the boreal to subtropics. By predicting terrestrial resource support from within-lake and catchment-level characteristics, we found that half of all consumer observations that is, the median were composed of at least 42% terrestrially derived material. In general, terrestrial support of zooplankton was greatest in lakes with large physical and hydrological connections to catchments that were rich in aboveground and belowground organic matter. However, some consumers responded less strongly to terrestrial resources where within-lake production was elevated. Our study shows that multiple mechanisms drive widespread cross-ecosystem support of aquatic consumers across Northern Hemisphere lakes and suggests that changes in terrestrial landscapes will influence ecosystem processes well beyond their boundaries. PMID:28345035

  19. Trophic transfer of metals along freshwater food webs: Evidence of cadmium biomagnification in nature

    USGS Publications Warehouse

    Croteau, M.-N.; Luoma, S.N.; Stewart, A.R.

    2005-01-01

    We conducted a study with cadmium (Cd) and copper (Cu) in the delta of San Francisco Bay, using nitrogen and carbon stable isotopes to identify trophic position and food web structure. Cadmium is progressively enriched among trophic levels in discrete epiphyte-based food webs composed of macrophyte-dwelling invertebrates (the first link being epiphytic algae) and fishes (the first link being gobies). Cadmium concentrations were biomagnified 15 times within the scope of two trophic links in both food webs. Trophic enrichment in invertebrates was twice that of fishes. No tendency toward trophic-level enrichment was observed for Cu, regardless of whether organisms were sorted by food web or treated on a taxonomic basis within discrete food webs. The greatest toxic effects of Cd are likely to occur with increasing trophic positions, where animals are ingesting Cd-rich prey (or food). In Franks Tract this occurs within discrete food chains composed of macrophyte-dwelling invertebrates or fishes inhabiting submerged aquatic vegetation. Unraveling ecosystem complexity is necessary before species most exposed and at risk can be identified. ?? 2005, by the American Society of Limnology and Oceanography, Inc.

  20. The role of microorganisms in a planktonic food web of a floodplain lake.

    PubMed

    Segovia, Bianca Trevizan; Pereira, Danielle Goeldner; Bini, Luis Mauricio; de Meira, Bianca Ramos; Nishida, Verônica Sayuri; Lansac-Tôha, Fabio Amodêo; Velho, Luiz Felipe Machado

    2015-02-01

    Food webs include complex ecological interactions that define the flow of matter and energy, and are fundamental in understanding the functioning of an ecosystem. Temporal variations in the densities of communities belonging to the planktonic food web (i.e., microbial: bacteria, flagellate, and ciliate; and grazing: zooplankton and phytoplankton) were investigated, aiming to clarify the interactions between these organisms and the dynamics of the planktonic food web in a floodplain lake. We hypothesized that hydrological pulse determines the path of matter and energy flow through the planktonic food web of this floodplain lake. Data were collected monthly from March 2007 to February 2008 at three different sites in Guaraná Lake (Mato Grosso do Sul State, Brazil). The path analysis provided evidence that the dynamics of the planktonic food web was strongly influenced by the hydrological pulse. The high-water period favored interactions among the organisms of the microbial loop, rather than their relationships with zooplankton and phytoplankton. Therefore, in this period, the strong interaction among the organisms of the grazing food chain suggests that the microbial loop functions as a sink of matter and energy. In turn, in the low-water period, higher primary productivity appeared to favor different interactions between the components of the grazing food chain and microorganisms, which would function as a link to the higher trophic levels.

  1. Stable nitrogen isotopic composition of amino acids reveals food web structure in stream ecosystems.

    PubMed

    Ishikawa, Naoto F; Kato, Yoshikazu; Togashi, Hiroyuki; Yoshimura, Mayumi; Yoshimizu, Chikage; Okuda, Noboru; Tayasu, Ichiro

    2014-07-01

    The stable N isotopic composition of individual amino acids (SIAA) has recently been used to estimate trophic positions (TPs) of animals in several simple food chain systems. However, it is unknown whether the SIAA is applicable to more complex food web analysis. In this study we measured the SIAA of stream macroinvertebrates, fishes, and their potential food sources (periphyton and leaf litter of terrestrial C3 plants) collected from upper and lower sites in two streams having contrasting riparian landscapes. The stable N isotope ratios of glutamic acid and phenylalanine confirmed that for primary producers (periphyton and C3 litter) the TP was 1, and for primary consumers (e.g., mayfly and caddisfly larvae) it was 2. We built a two-source mixing model to estimate the relative contributions of aquatic and terrestrial sources to secondary and higher consumers (e.g., stonefly larva and fishes) prior to the TP calculation. The estimated TPs (2.3-3.5) roughly corresponded to their omnivorous and carnivorous feeding habits, respectively. We found that the SIAA method offers substantial advantages over traditional bulk method for food web analysis because it defines the food web structure based on the metabolic pathway of amino groups, and can be used to estimate food web structure under conditions where the bulk method cannot be used. Our result provides evidence that the SIAA method is applicable to the analysis of complex food webs, where heterogeneous resources are mixed.

  2. Interactive effects of warming, eutrophication and size structure: impacts on biodiversity and food-web structure.

    PubMed

    Binzer, Amrei; Guill, Christian; Rall, Björn C; Brose, Ulrich

    2016-01-01

    Warming and eutrophication are two of the most important global change stressors for natural ecosystems, but their interaction is poorly understood. We used a dynamic model of complex, size-structured food webs to assess interactive effects on diversity and network structure. We found antagonistic impacts: Warming increases diversity in eutrophic systems and decreases it in oligotrophic systems. These effects interact with the community size structure: Communities of similarly sized species such as parasitoid-host systems are stabilized by warming and destabilized by eutrophication, whereas the diversity of size-structured predator-prey networks decreases strongly with warming, but decreases only weakly with eutrophication. Nonrandom extinction risks for generalists and specialists lead to higher connectance in networks without size structure and lower connectance in size-structured communities. Overall, our results unravel interactive impacts of warming and eutrophication and suggest that size structure may serve as an important proxy for predicting the community sensitivity to these global change stressors.

  3. Global Patterns in Ecological Indicators of Marine Food Webs: A Modelling Approach

    PubMed Central

    Heymans, Johanna Jacomina; Coll, Marta; Libralato, Simone; Morissette, Lyne; Christensen, Villy

    2014-01-01

    Background Ecological attributes estimated from food web models have the potential to be indicators of good environmental status given their capabilities to describe redundancy, food web changes, and sensitivity to fishing. They can be used as a baseline to show how they might be modified in the future with human impacts such as climate change, acidification, eutrophication, or overfishing. Methodology In this study ecological network analysis indicators of 105 marine food web models were tested for variation with traits such as ecosystem type, latitude, ocean basin, depth, size, time period, and exploitation state, whilst also considering structural properties of the models such as number of linkages, number of living functional groups or total number of functional groups as covariate factors. Principal findings Eight indicators were robust to model construction: relative ascendency; relative overhead; redundancy; total systems throughput (TST); primary production/TST; consumption/TST; export/TST; and total biomass of the community. Large-scale differences were seen in the ecosystems of the Atlantic and Pacific Oceans, with the Western Atlantic being more complex with an increased ability to mitigate impacts, while the Eastern Atlantic showed lower internal complexity. In addition, the Eastern Pacific was less organised than the Eastern Atlantic although both of these systems had increased primary production as eastern boundary current systems. Differences by ecosystem type highlighted coral reefs as having the largest energy flow and total biomass per unit of surface, while lagoons, estuaries, and bays had lower transfer efficiencies and higher recycling. These differences prevailed over time, although some traits changed with fishing intensity. Keystone groups were mainly higher trophic level species with mostly top-down effects, while structural/dominant groups were mainly lower trophic level groups (benthic primary producers such as seagrass and macroalgae

  4. Mechanisms affecting recovery in an upwelling food web: The case of the southern Humboldt

    NASA Astrophysics Data System (ADS)

    Neira, Sergio; Moloney, Coleen L.; Cury, Philippe; Mullon, Christian; Christensen, Villy

    2009-12-01

    Although bottom-up forcing and overfishing are known to induce shifts in ecosystem states, system changes and their reversibility under each factor are still poorly understood. In this paper, dynamic food web simulations are conducted to evaluate when and why ecological thresholds may be exceeded, and whether bottom-up forcing or fishing is more likely to induce irreversible ecosystem states. Simulations are conducted using a calibrated food web model of the upwelling system off central Chile (33-39°S) and the Ecopath with Ecosim software version 5.1. The effects of fishing scenarios are explored by changing fishing mortality according to trophic level. The effects of bottom-up forcing scenarios are explored by changing phytoplankton biomass, as a function of sea temperature, at El Niño Southern Oscillation (ENSO) and decadal scales. Simulations are carried out for 150 years and impacts, system recovery and regime shifts from each scenario are evaluated using trophodynamic indicators and limit reference points for biomass of functional groups as proxies of food web state and ecological thresholds, respectively. Proportionally distributed fishing along trophic levels is the least harmful fishing scenario, resulting in biomass limit reference points rarely being exceeded and high system recovery. Concentrating fishing at higher and lower trophic levels more likely causes reference points to be exceeded and induces ecosystem changes with low-to-medium recovery potential. No limit reference points are exceeded (or regime shift induced) under ENSO-scale bottom-up forcing. Decadal scale bottom-up forcing has different effects on the system depending on the sequence in which the high and low phytoplankton biomass periods are simulated. A shift from low phytoplankton biomass towards high phytoplankton biomass does not result in biomass limit reference points being exceeded, whereas the opposite sequence results in a large number of limit reference points being exceeded

  5. Food web structure of sandy beaches: Temporal and spatial variation using stable isotope analysis

    NASA Astrophysics Data System (ADS)

    Bergamino, Leandro; Lercari, Diego; Defeo, Omar

    2011-03-01

    The food web structure of two sandy beach ecosystems with contrasting morphodynamics (dissipative vs. reflective) was examined using stable carbon (δ 13C) and nitrogen (δ 15N) isotope analysis. Organic matter sources (POM: particulate organic matter; SOM: sediment organic matter) and consumers (zooplankton, benthic invertebrates and fishes) were sampled seasonally in both sandy beaches. Food webs significantly differed between beaches: even though both webs were mainly supported by POM, depleted δ 13C and δ 15N values for food sources and consumers were found in the dissipative system (following the reverse pattern in δ 13C values for consumers) for all the four seasons. Primary consumers (zooplankton and benthic invertebrates) use different organic matter sources on each beach and these differences are propagated up in the food web. The higher productivity found in the dissipative beach provided a significant amount of food for primary consumers, notably suspension feeders. Thus, the dissipative beach supported a more complex food web with more trophic links and a higher number of prey and top predators than the reflective beach. Morphodynamic factors could explain the contrasting differences in food web structure. The high degree of retention (nutrients and phytoplankton) recorded for the surf zone of the dissipative beach would result in the renewed accumulation of POM that sustains a more diverse and richer fauna than the reflective beach. Further studies directed to assess connections between the macroscopic food web, the surf-zone microbial loop and the interstitial compartment will provide a deeper understanding on the functioning of sandy beach ecosystems.

  6. Benthic community responses to macroalgae invasions in seagrass beds: Diversity, isotopic niche and food web structure at community level

    NASA Astrophysics Data System (ADS)

    Deudero, S.; Box, A.; Vázquez-Luis, M.; Arroyo, N. L.

    2014-04-01

    Trophic paths between species are a useful tool for analysing the impact of species invasions of a biotic community. Species invasions produce changes at trophic level and diversity shifts by replacing native species with species of similar ecological niche. This study focused on the effects of macroalgal invasions on seagrass ecosystems. We conducted two - year bimonthly sampling of a pristine Posidonia oceanica seagrass meadow and dead matte colonized by three Caulerpa species bimonthly. The largest changes in faunal composition were found in meadows colonized by Caulerpa prolifera, where major differences in infaunal taxonomic distinctness were apparent. On the other hand, the infaunal community was quite similar between the two invasive Caulerpa species (Caulerpa taxifolia and Caulerpa racemosa). The isotopic niche based on the main trophic guilds established using stable isotope signatures at community level resulted in a highly compacted and 15N-enriched C. prolifera food web structure, indicating high overlap of food source utilization among faunal components, which is typical of degraded systems. Conversely, the P. oceanica ecosystem presented the most complex food web, while the influence of the 2 invasive species were similar. An attempt to reconstruct the food web at each vegetated habitat revealed high trophic linkages among the different trophic levels with a continuous transition among them by the various trophic guilds suggesting an adaptation response of the different organisms to the new habitat forming species.

  7. Biological impacts of local vs. regional land use on a small tributary of the Seine River (France): insights from a food web approach based on stable isotopes.

    PubMed

    Hette-Tronquart, Nicolas; Oberdorff, Thierry; Tales, Evelyne; Zahm, Amandine; Belliard, Jérôme

    2017-03-23

    As part of the landscape, streams are influenced by land use. Here, we contributed to the understanding of the biological impacts of land use on streams, investigating how landscape effects vary with spatial scales (local vs. regional). We adopted a food web approach integrating both biological structure and functioning, to focus on the overall effect of land use on stream biocœnosis. We selected 17 sites of a small tributary of the Seine River (France) for their contrasted land use, and conducted a natural experiment by sampling three organic matter sources, three macroinvertebrate taxa, and most of the fish community. Using stable isotope analysis, we calculated three food web metrics evaluating two major dimensions of the trophic diversity displayed by the fish community: (i) the diversity of exploited resources and (ii) the trophic level richness. The idea was to examine whether (1) land-use effects varied according to spatial scales, (2) land use affected food webs through an effect on community structure and (3) land use affected food webs through an effect on available resources. Beside an increase in trophic diversity from upstream to downstream, our empirical data showed that food webs were influenced by land use in the riparian corridors (local scale). The effect was complex, and depended on site's position along the upstream-downstream gradient. By contrast, land use in the catchment (regional scale) did not influence stream biocœnosis. At the local scale, community structure was weakly influenced by land use, and thus played a minor role in explaining food web modifications. Our results suggested that the amount of available resources at the base of the food web was partly responsible for food web modifications. In addition, changes in biological functioning (i.e. feeding interactions) can also explain another part of the land-use effect. These results highlight the role played by the riparian corridors as a buffer zone, and advocate that riparian

  8. Biomass Reallocation between Juveniles and Adults Mediates Food Web Stability by Distributing Energy Away from Strong Interactions.

    PubMed

    Caskenette, Amanda L; McCann, Kevin S

    2017-01-01

    Ecological theory has uncovered dynamical differences between food web modules (i.e. low species food web configurations) with only species-level links and food web modules that include within-species links (e.g. non-feeding links between mature and immature individuals) and has argued that these differences ought to cause food web theory that includes within-species links to contrast with classical food web theory. It is unclear, however, if life-history will affect the observed connection between interaction strength and stability in species-level theory. We show that when the predator in a species-level food chain is split into juvenile and adult stages using a simple nested approach, stage-structure can mute potentially strong interactions through the transfer of biomass within a species. Within-species biomass transfer distributes energy away from strong interactions promoting increased system stability consistent with classical food web theory.

  9. Biomass Reallocation between Juveniles and Adults Mediates Food Web Stability by Distributing Energy Away from Strong Interactions

    PubMed Central

    Caskenette, Amanda L.; McCann, Kevin S.

    2017-01-01

    Ecological theory has uncovered dynamical differences between food web modules (i.e. low species food web configurations) with only species-level links and food web modules that include within-species links (e.g. non-feeding links between mature and immature individuals) and has argued that these differences ought to cause food web theory that includes within-species links to contrast with classical food web theory. It is unclear, however, if life-history will affect the observed connection between interaction strength and stability in species-level theory. We show that when the predator in a species-level food chain is split into juvenile and adult stages using a simple nested approach, stage-structure can mute potentially strong interactions through the transfer of biomass within a species. Within-species biomass transfer distributes energy away from strong interactions promoting increased system stability consistent with classical food web theory. PMID:28114339

  10. Food Chains & Webs. A Multimedia CD-ROM. [CD-ROM].

    ERIC Educational Resources Information Center

    2001

    This CD-ROM is designed for classroom and individual use to teach and learn about food chains and food webs. Integrated animations, custom graphics, three-dimensional representations, photographs, and sound are featured for use in user-controlled activities. Interactive lessons are available to reinforce the subject material. Pre- and post-testing…

  11. Reconciling the role of terrestrial leaves in pond food webs: a whole-ecosystem experiment.

    PubMed

    Holgerson, Meredith A; Post, David M; Skelly, David K

    2016-07-01

    Terrestrial carbon and nutrients can subsidize the detrital pool of freshwater ecosystems; yet, the importance of terrestrial subsidies to lake and pond food webs is uncertain and debated. Terrestrial detritus is expected to have the greatest impact on food webs when water bodies are small and shallow with low levels of incident light. Temporary forested ponds fit this description and are often assumed to have a leaf detritus-based food web, but this has not been quantified. In a whole-ecosystem experiment, we traced the flow of isotopically enriched leaf litter to primary producers and consumers in a small, forested pond. We found that terrestrial leaves provided nutrients to algae, offering an indirect pathway in which leaf litter can enter the food web. Terrestrial leaves were also consumed directly, and larval caddisfly (Limnephilus sp.) shredders likely mobilized leaf nutrients to other consumers, a process overlooked in many previous small-scale experiments that did not incorporate shredders. Unexpectedly, most consumers relied heavily upon algal food pathways despite low light and net heterotrophic conditions. Overall, our study highlights the interconnectedness of algal and leaf litter pathways in small pond food webs, and emphasizes that algal pathways are prevalent and important even in small, shaded ponds with high loads of terrestrial leaf litter.

  12. Trophic Magnification of Parabens and Their Metabolites in a Subtropical Marine Food Web.

    PubMed

    Xue, Xiaohong; Xue, Jingchuan; Liu, Wenbin; Adams, Douglas H; Kannan, Kurunthachalam

    2017-01-17

    Despite the widespread use of parabens in a range of consumer products, little is known about bioaccumulation of these chemicals in aquatic environments. In this study, six parabens and four of their common metabolites were measured in abiotic (water, sediment) and biotic (fish including sharks, invertebrates, plants) samples collected from a subtropical marine food web in coastal Florida. Methyl paraben (MeP) was found in all abiotic (100%) and a majority of biotic (87%) samples. 4-Hydroxy benzoic acid (4-HB) was the most abundant metabolite, found in 97% of biotic and all abiotic samples analyzed. The food chain accumulation of MeP and 4-HB was investigated for this food web. The trophic magnification factor (TMF) of MeP was estimated to be 1.83, which suggests considerable bioaccumulation and biomagnification of this compound in the marine food web. In contrast, a low TMF value was found for 4-HB (0.30), indicating that this compound is metabolized and excreted along the food web. This is the first study to document the widespread occurrence of parabens and their metabolites in fish, invertebrates, seagrasses, marine macroalgae, mangroves, seawater, and ocean sediments and to elucidate biomagnification potential of MeP in a marine food web.

  13. The meaning of functional trait composition of food webs for ecosystem functioning.

    PubMed

    Gravel, Dominique; Albouy, Camille; Thuiller, Wilfried

    2016-05-19

    There is a growing interest in using trait-based approaches to characterize the functional structure of animal communities. Quantitative methods have been derived mostly for plant ecology, but it is now common to characterize the functional composition of various systems such as soils, coral reefs, pelagic food webs or terrestrial vertebrate communities. With the ever-increasing availability of distribution and trait data, a quantitative method to represent the different roles of animals in a community promise to find generalities that will facilitate cross-system comparisons. There is, however, currently no theory relating the functional composition of food webs to their dynamics and properties. The intuitive interpretation that more functional diversity leads to higher resource exploitation and better ecosystem functioning was brought from plant ecology and does not apply readily to food webs. Here we appraise whether there are interpretable metrics to describe the functional composition of food webs that could foster a better understanding of their structure and functioning. We first distinguish the various roles that traits have on food web topology, resource extraction (bottom-up effects), trophic regulation (top-down effects), and the ability to keep energy and materials within the community. We then discuss positive effects of functional trait diversity on food webs, such as niche construction and bottom-up effects. We follow with a discussion on the negative effects of functional diversity, such as enhanced competition (both exploitation and apparent) and top-down control. Our review reveals that most of our current understanding of the impact of functional trait diversity on food web properties and functioning comes from an over-simplistic representation of network structure with well-defined levels. We, therefore, conclude with propositions for new research avenues for both theoreticians and empiricists.

  14. Idiosyncratic responses of grizzly bear habitat to climate change based on projected food resource changes.

    PubMed

    Roberts, David R; Nielsen, Scott E; Stenhouse, Gordon B

    2014-07-01

    Climate change vulnerability assessments for species of conservation concern often use species distribution and ecological niche modeling to project changes in habitat. One of many assumptions of these approaches is that food web dependencies are consistent in time and environmental space. Species at higher trophic levels that rely on the availability of species at lower trophic levels as food may be sensitive to extinction cascades initiated by changes in the habitat of key food resources. Here we assess climate change vulnerability for Ursus arctos (grizzly bears) in the southern Canadian Rocky Mountains using projected changes to 17 of the most commonly consumed plant food items. We used presence-absence information from 7088 field plots to estimate ecological niches and to project changes in future distributions of each species. Model projections indicated idiosyncratic responses among food items. Many food items persisted or even increased, although several species were found to be vulnerable based on declines or geographic shifts in suitable habitat. These included Hedysarum alpinum (alpine sweet vetch), a critical spring and autumn root-digging resource when little else is available. Potential habitat loss was also identified for three fruiting species of lower importance to bears: Empetrum nigrum (crowberry), Vaccinium scoparium (grouseberry), and Fragaria virginiana (strawberry). A general trend towards uphill migration of bear foods may result in higher vulnerability to bear populations at low elevations, which are also those that are most likely to have human-bear conflict problems. Regardless, a wide diet breadth of grizzly bears, as well as wide environmental niches of most food items, make climate change a much lower threat to grizzly bears than other bear species such as polar bears and panda bears. We cannot exclude, however, future alterations in human behavior and land use resulting from climate change that may reduce survival rates.

  15. FoodPro: A Web-Based Tool for Evaluating Covariance and Correlation NMR Spectra Associated with Food Processes.

    PubMed

    Chikayama, Eisuke; Yamashina, Ryo; Komatsu, Keiko; Tsuboi, Yuuri; Sakata, Kenji; Kikuchi, Jun; Sekiyama, Yasuyo

    2016-10-19

    Foods from agriculture and fishery products are processed using various technologies. Molecular mixture analysis during food processing has the potential to help us understand the molecular mechanisms involved, thus enabling better cooking of the analyzed foods. To date, there has been no web-based tool focusing on accumulating Nuclear Magnetic Resonance (NMR) spectra from various types of food processing. Therefore, we have developed a novel web-based tool, FoodPro, that includes a food NMR spectrum database and computes covariance and correlation spectra to tasting and hardness. As a result, FoodPro has accumulated 236 aqueous (extracted in D₂O) and 131 hydrophobic (extracted in CDCl₃) experimental bench-top 60-MHz NMR spectra, 1753 tastings scored by volunteers, and 139 hardness measurements recorded by a penetrometer, all placed into a core database. The database content was roughly classified into fish and vegetable groups from the viewpoint of different spectrum patterns. FoodPro can query a user food NMR spectrum, search similar NMR spectra with a specified similarity threshold, and then compute estimated tasting and hardness, covariance, and correlation spectra to tasting and hardness. Querying fish spectra exemplified specific covariance spectra to tasting and hardness, giving positive covariance for tasting at 1.31 ppm for lactate and 3.47 ppm for glucose and a positive covariance for hardness at 3.26 ppm for trimethylamine N-oxide.

  16. FoodPro: A Web-Based Tool for Evaluating Covariance and Correlation NMR Spectra Associated with Food Processes

    PubMed Central

    Chikayama, Eisuke; Yamashina, Ryo; Komatsu, Keiko; Tsuboi, Yuuri; Sakata, Kenji; Kikuchi, Jun; Sekiyama, Yasuyo

    2016-01-01

    Foods from agriculture and fishery products are processed using various technologies. Molecular mixture analysis during food processing has the potential to help us understand the molecular mechanisms involved, thus enabling better cooking of the analyzed foods. To date, there has been no web-based tool focusing on accumulating Nuclear Magnetic Resonance (NMR) spectra from various types of food processing. Therefore, we have developed a novel web-based tool, FoodPro, that includes a food NMR spectrum database and computes covariance and correlation spectra to tasting and hardness. As a result, FoodPro has accumulated 236 aqueous (extracted in D2O) and 131 hydrophobic (extracted in CDCl3) experimental bench-top 60-MHz NMR spectra, 1753 tastings scored by volunteers, and 139 hardness measurements recorded by a penetrometer, all placed into a core database. The database content was roughly classified into fish and vegetable groups from the viewpoint of different spectrum patterns. FoodPro can query a user food NMR spectrum, search similar NMR spectra with a specified similarity threshold, and then compute estimated tasting and hardness, covariance, and correlation spectra to tasting and hardness. Querying fish spectra exemplified specific covariance spectra to tasting and hardness, giving positive covariance for tasting at 1.31 ppm for lactate and 3.47 ppm for glucose and a positive covariance for hardness at 3.26 ppm for trimethylamine N-oxide. PMID:27775560

  17. Climate alters intraspecific variation in copepod effect traits through pond food webs.

    PubMed

    Charette, Cristina; Derry, Alison M

    2016-05-01

    Essential fatty acids (EFAs) are primarily generated by phytoplankton in aquatic ecosystems, and can limit the growth, development, and reproduction of higher consumers. Among the most critical of the EFAs are highly unsaturated fatty acids (HUFAs), which are only produced by certain groups of phytoplankton. Changing environmental conditions can alter phytoplankton community and fatty acid composition and affect the HUFA content of higher trophic levels. Almost no research has addressed intraspecific variation in HUFAs in zooplankton, nor intraspecific relationships of HUFAs with body size and fecundity. This is despite that intraspecific variation in HUFAs can exceed interspecific variation and that intraspecific trait variation in body size and fecundity is increasingly recognized to have an important role in food web ecology (effect traits). Our study addressed the relative influences of abiotic selection and food web effects associated with climate change on intraspecific differences and interrelationships between HUFA content, body size, and fecundity of freshwater copepods. We applied structural equation modeling and regression analyses to intraspecific variation in a dominant calanoid copepod, Leptodiatomus minutus, among a series of shallow north-temperate ponds. Climate-driven diurnal temperature fluctuations favored the coexistence of diversity of phytoplankton groups with different temperature optima and nutritive quality. This resulted in unexpected positive relationships between temperature, copepod DHA content and body size. Temperature correlated positively with diatom biovolume, and mediated relationships between copepod HUFA content and body size, and between copepod body size and fecundity. The presence of brook trout further accentuated these positive effects in warm ponds, likely through nutrient cycling and stimulation of phytoplankton resources. Climate change may have previously unrecognized positive effects on freshwater copepod DHA content

  18. Invasive crayfish as vectors of mercury in freshwater food webs of the Pacific Northwest.

    PubMed

    Johnson, Branden L; Willacker, James J; Eagles-Smith, Collin A; Pearl, Christopher A; Adams, Michael J

    2014-11-01

    Invasive species are important drivers of environmental change in aquatic ecosystems and can alter habitat characteristics, community composition, and ecosystem energetics. Such changes have important implications for many ecosystem processes, including the bioaccumulation and biomagnification of contaminants through food webs. Mercury concentrations were measured in 2 nonnative and 1 native crayfish species from western Oregon (USA). Nonnative red swamp crayfish had mercury concentrations similar to those in native signal crayfish (0.29 ± 0.05 µg/g dry wt and 0.36 ± 0.06 µg/g dry wt, respectively), whereas the nonnative ringed crayfish had lower mercury concentrations (0.10 ± 0.02 µg/g dry wt) than either of the other species. The mean energy content of muscle was similar between the native signal crayfish and nonnative ringed crayfish but was significantly higher in the nonnative red swamp crayfish. Across species, mercury concentrations were negatively correlated with energy density. Such energetic differences could exacerbate changes in mercury transfer through trophic pathways of food webs, especially via alterations to the growth dynamics of consumers. Thus, it is important to consider the role of energy content in determining effective mercury exposure even when mercury concentrations on a per-unit mass basis do not differ between species. Environ Toxicol Chem 2014;33:2639-2645. Published 2014 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US Government work and as such, is in the public domain in the United States of America.

  19. An innovative statistical approach to constructing a readily comprehensible food web for a demersal fish community

    NASA Astrophysics Data System (ADS)

    French, Ben; Clarke, K. Robert; Platell, Margaret E.; Potter, Ian C.

    2013-07-01

    Many food webs are so complex that it is difficult to distinguish the relationships between predators and their prey. We have therefore developed an approach that produces a food web which clearly demonstrates the strengths of the relationships between the predator guilds of demersal fish and their prey guilds in a coastal ecosystem. Subjecting volumetric dietary data for 35 abundant predators along the lower western Australia coast to cluster analysis and the SIMPROF routine separated the various species × length class combinations into 14 discrete predator guilds. Following nMDS ordination, the sequence of points for these predator guilds represented a 'trophic' hierarchy. This demonstrated that, with increasing body size, several species progressed upwards through this hierarchy, reflecting a marked change in diet, whereas others remained within the same guild. A novel use of cluster analysis and SIMPROF then identified each group of prey that was ingested in a common pattern across the full suite of predator guilds. This produced 12 discrete groups of taxa (prey guilds) that each typically comprised similar ecological/functional prey, which were then also aligned in a hierarchy. The hierarchical arrangements of the predator and prey guilds were plotted against each other to show the percentage contribution of each prey guild to the diet of each predator guild. The resultant shade plot demonstrates quantitatively how food resources are spread among the fish species and revealed that two prey guilds, one containing cephalopods and teleosts and the other small benthic/epibenthic crustaceans and polychaetes, were consumed by all predator guilds.

  20. Changing Academic Teaching with Web 2.0 Technologies

    ERIC Educational Resources Information Center

    Newland, Barbara; Byles, Linda

    2014-01-01

    Academic teaching can change with the use of Web 2.0 technologies, such as blogs and wikis, as these enable a different pedagogical approach through collaborative learning and the social construction of knowledge. Student expectations of their university learning experience have changed as they expect e-learning to be part of the learning…

  1. Trends That Could Change School Food Service.

    ERIC Educational Resources Information Center

    VanEgmond-Pannell, Dorothy

    1986-01-01

    Among the 10 megatrends that will affect school food service in the future are population changes; computerized and automated kitchens; cost increases; school districts contracting to serve other community groups; fewer federal government controls; and higher teacher salaries, forcing changes in how students are taught. (MLF)

  2. The zooplankton food web under East Antarctic pack ice - A stable isotope study

    NASA Astrophysics Data System (ADS)

    Jia, Zhongnan; Swadling, Kerrie M.; Meiners, Klaus M.; Kawaguchi, So; Virtue, Patti

    2016-09-01

    Understanding how sea ice serves zooplankton species during the food-limited season is crucial information to evaluate the potential responses of pelagic food webs to changes in sea-ice conditions in the Southern Ocean. Stable isotope analyses (13C/12C and 15N/14N) were used to compare the dietary preferences and trophic relationships of major zooplankton species under pack ice during two winter-spring transitions (2007 and 2012). During sampling, furcilia of Euphausia superba demonstrated dietary plasticity between years, herbivory when feeding on sea-ice biota, and with a more heterotrophic diet when feeding from both the sea ice and the water column. Carbon isotope signatures suggested that the pteropod Limacina helicina, small copepods Oithona spp., ostracods and amphipods relied heavily on sea-ice biota. Post larval E. superba and omnivorous krill Thysanoessa macrura consumed both water column and ice biota, but further investigations are needed to estimate the contribution from each source. Large copepods and chaetognaths overwintered on a water column-based diet. Our study suggests that warm and permeable sea ice is more likely to provide food for zooplankton species under the ice than the colder ice.

  3. Rapid evolution buffers ecosystem impacts of viruses in a microbial food web.

    PubMed

    Lennon, Jay T; Martiny, Jennifer B H

    2008-11-01

    Predation and parasitism often regulate population dynamics, community interactions, and ecosystem functioning. The strength of these top-down pressures is variable, however, and may be influenced by both ecological and evolutionary processes. We conducted a chemostat experiment to assess the direct and indirect effects of viruses on a marine microbial food web comprised of an autotrophic host (Synechococcus) and non-target heterotrophic bacteria. Viruses dramatically altered the host population dynamics, which in turn influenced phosphorus resource availability and the stoichiometric allocation of nutrients into microbial biomass. These virus effects diminished with time, but could not be attributed to changes in the abundance or composition of heterotrophic bacteria. Instead, attenuation of the virus effects coincided with the detection of resistant host phenotypes, suggesting that rapid evolution buffered the effect of viruses on nutrient cycling. Our results demonstrate that evolutionary processes are important for community dynamics and ecosystem processes on ecologically relevant time scales.

  4. How habitat-modifying organisms structure the food web of two coastal ecosystems

    PubMed Central

    van der Zee, Els M.; Angelini, Christine; Govers, Laura L.; Christianen, Marjolijn J. A.; Altieri, Andrew H.; van der Reijden, Karin J.; Silliman, Brian R.; van de Koppel, Johan; van der Geest, Matthijs; van Gils, Jan A.; van der Veer, Henk W.; Piersma, Theunis; de Ruiter, Peter C.; Olff, Han; van der Heide, Tjisse

    2016-01-01

    The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity. PMID:26962135

  5. Soil food web properties explain ecosystem services across European land use systems

    PubMed Central

    de Vries, Franciska T.; Thébault, Elisa; Liiri, Mira; Birkhofer, Klaus; Tsiafouli, Maria A.; Bjørnlund, Lisa; Bracht Jørgensen, Helene; Brady, Mark Vincent; Christensen, Søren; de Ruiter, Peter C.; d’Hertefeldt, Tina; Frouz, Jan; Hedlund, Katarina; Hemerik, Lia; Hol, W. H. Gera; Hotes, Stefan; Mortimer, Simon R.; Setälä, Heikki; Sgardelis, Stefanos P.; Uteseny, Karoline; van der Putten, Wim H.; Wolters, Volkmar; Bardgett, Richard D.

    2013-01-01

    Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic locations, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world. PMID:23940339

  6. Soil food web properties explain ecosystem services across European land use systems.

    PubMed

    de Vries, Franciska T; Thébault, Elisa; Liiri, Mira; Birkhofer, Klaus; Tsiafouli, Maria A; Bjørnlund, Lisa; Bracht Jørgensen, Helene; Brady, Mark Vincent; Christensen, Søren; de Ruiter, Peter C; d'Hertefeldt, Tina; Frouz, Jan; Hedlund, Katarina; Hemerik, Lia; Hol, W H Gera; Hotes, Stefan; Mortimer, Simon R; Setälä, Heikki; Sgardelis, Stefanos P; Uteseny, Karoline; van der Putten, Wim H; Wolters, Volkmar; Bardgett, Richard D

    2013-08-27

    Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic locations, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world.

  7. How habitat-modifying organisms structure the food web of two coastal ecosystems.

    PubMed

    van der Zee, Els M; Angelini, Christine; Govers, Laura L; Christianen, Marjolijn J A; Altieri, Andrew H; van der Reijden, Karin J; Silliman, Brian R; van de Koppel, Johan; van der Geest, Matthijs; van Gils, Jan A; van der Veer, Henk W; Piersma, Theunis; de Ruiter, Peter C; Olff, Han; van der Heide, Tjisse

    2016-03-16

    The diversity and structure of ecosystems has been found to depend both on trophic interactions in food webs and on other species interactions such as habitat modification and mutualism that form non-trophic interaction networks. However, quantification of the dependencies between these two main interaction networks has remained elusive. In this study, we assessed how habitat-modifying organisms affect basic food web properties by conducting in-depth empirical investigations of two ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows. Results reveal that habitat-modifying species, through non-trophic facilitation rather than their trophic role, enhance species richness across multiple trophic levels, increase the number of interactions per species (link density), but decrease the realized fraction of all possible links within the food web (connectance). Compared to the trophic role of the most highly connected species, we found this non-trophic effects to be more important for species richness and of more or similar importance for link density and connectance. Our findings demonstrate that food webs can be fundamentally shaped by interactions outside the trophic network, yet intrinsic to the species participating in it. Better integration of non-trophic interactions in food web analyses may therefore strongly contribute to their explanatory and predictive capacity.

  8. Legacy effects of drought on plant growth and the soil food web.

    PubMed

    de Vries, Franciska Trijntje; Liiri, Mira E; Bjørnlund, Lisa; Setälä, Heikki M; Christensen, Søren; Bardgett, Richard D

    2012-11-01

    Soils deliver important ecosystem services, such as nutrient provision for plants and the storage of carbon (C) and nitrogen (N), which are greatly impacted by drought. Both plants and soil biota affect soil C and N availability, which might in turn affect their response to drought, offering the potential to feed back on each other's performance. In a greenhouse experiment, we compared legacy effects of repeated drought on plant growth and the soil food web in two contrasting land-use systems: extensively managed grassland, rich in C and with a fungal-based food web, and intensively managed wheat lower in C and with a bacterial-based food web. Moreover, we assessed the effect of plant presence on the recovery of the soil food web after drought. Drought legacy effects increased plant growth in both systems, and a plant strongly reduced N leaching. Fungi, bacteria, and their predators were more resilient after drought in the grassland soil than in the wheat soil. The presence of a plant strongly affected the composition of the soil food web, and alleviated the effects of drought for most trophic groups, regardless of the system. This effect was stronger for the bottom trophic levels, whose resilience was positively correlated to soil available C. Our results show that plant belowground inputs have the potential to affect the recovery of belowground communities after drought, with implications for the functions they perform, such as C and N cycling.

  9. Stability of complex food webs: resilience, resistance and the average interaction strength.

    PubMed

    Vallina, Sergio M; Le Quéré, Corinne

    2011-03-07

    In the face of stochastic climatic perturbations, the overall stability of an ecosystem will be determined by the balance between its resilience and its resistance, but their relative importance is still unknown. Using aquatic food web models we study ecosystem stability as a function of food web complexity. We measured three dynamical stability properties: resilience, resistance, and variability. Specifically, we evaluate how a decrease in the strength of predator-prey interactions with food web complexity, reflecting a decrease in predation efficiency with the number of prey per predator, affects the overall stability of the ecosystem. We find that in mass conservative ecosystems, a lower interaction strength slows down the mass cycling rate in the system and this increases its resistance to perturbations of the growth rate of primary producers. Furthermore, we show that the overall stability of the food webs is mostly given by their resistance, and not by their resilience. Resilience and resistance display opposite trends, although they are shown not to be simply opposite concepts but rather independent properties. The ecological implication is that weaker predator-prey interactions in closed ecosystems can stabilize food web dynamics by increasing its resistance to climatic perturbations.

  10. Linking water quality and quantity in environmental flow assessment in deteriorated ecosystems: a food web view.

    PubMed

    Chen, He; Ma, Lekuan; Guo, Wei; Yang, Ying; Guo, Tong; Feng, Cheng

    2013-01-01

    Most rivers worldwide are highly regulated by anthropogenic activities through flow regulation and water pollution. Environmental flow regulation is used to reduce the effects of anthropogenic activities on aquatic ecosystems. Formulating flow alteration-ecological response relationships is a key factor in environmental flow assessment. Traditional environmental flow models are characterized by natural relationships between flow regimes and ecosystem factors. However, food webs are often altered from natural states, which disturb environmental flow assessment in such ecosystems. In ecosystems deteriorated by heavy anthropogenic activities, the effects of environmental flow regulation on species are difficult to assess with current modeling approaches. Environmental flow management compels the development of tools that link flow regimes and food webs in an ecosystem. Food web approaches are more suitable for the task because they are more adaptive for disordered multiple species in a food web deteriorated by anthropogenic activities. This paper presents a global method of environmental flow assessment in deteriorated aquatic ecosystems. Linkages between flow regimes and food web dynamics are modeled by incorporating multiple species into an ecosystem to explore ecosystem-based environmental flow management. The approach allows scientists and water resources managers to analyze environmental flows in deteriorated ecosystems in an ecosystem-based way.

  11. Linking Water Quality and Quantity in Environmental Flow Assessment in Deteriorated Ecosystems: A Food Web View

    PubMed Central

    Chen, He; Ma, Lekuan; Guo, Wei; Yang, Ying; Guo, Tong; Feng, Cheng

    2013-01-01

    Most rivers worldwide are highly regulated by anthropogenic activities through flow regulation and water pollution. Environmental flow regulation is used to reduce the effects of anthropogenic activities on aquatic ecosystems. Formulating flow alteration–ecological response relationships is a key factor in environmental flow assessment. Traditional environmental flow models are characterized by natural relationships between flow regimes and ecosystem factors. However, food webs are often altered from natural states, which disturb environmental flow assessment in such ecosystems. In ecosystems deteriorated by heavy anthropogenic activities, the effects of environmental flow regulation on species are difficult to assess with current modeling approaches. Environmental flow management compels the development of tools that link flow regimes and food webs in an ecosystem. Food web approaches are more suitable for the task because they are more adaptive for disordered multiple species in a food web deteriorated by anthropogenic activities. This paper presents a global method of environmental flow assessment in deteriorated aquatic ecosystems. Linkages between flow regimes and food web dynamics are modeled by incorporating multiple species into an ecosystem to explore ecosystem-based environmental flow management. The approach allows scientists and water resources managers to analyze environmental flows in deteriorated ecosystems in an ecosystem-based way. PMID:23894669

  12. Food web accumulation of cyclic siloxanes in Lake Mjøsa, Norway.

    PubMed

    Borgå, Katrine; Fjeld, Eirik; Kierkegaard, Amelie; McLachlan, Michael S

    2012-06-05

    The biomagnification of the cyclic volatile methyl siloxanes octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexatetrasiloxane (D6) was analyzed in the Lake Mjøsa food web in Norway from zooplankton and Mysis to planktivorous and piscivorous fish. The trophic magnification factor (TMF) for D5 was determined and compared with TMFs of several legacy contaminants: polychlorinated biphenyl (PCB) congeners 153 and 180, polybrominated diphenyl ether (PBDE) congeners 47 and 99, and p,p'-DDE. D5 showed TMF significantly greater than 1, implying food web biomagnification (TMF = 2.28, CI: 1.22-4.29). This contrasts with two studies that reported TMF < 1, which may reflect variability in TMF between food webs. The Lake Mjøsa D5 TMF was sensitive to the species included at the higher trophic level; whole food web TMF differed from TMF excluding smelt (Osmerus eperlanus) or brown trout (Salmo trutta) (TMF(-SMELT) = 1.62, CI: 0.96-2.72; TMF(-TROUT) = 3.58, CI: 1.82-7.03). For legacy contaminants (e.g., PCB-153 and PCB-180), the TMFs were less sensitive to the food web composition, and a better model fit was obtained compared to D5. The differences in biomagnification behavior between D5 and the legacy contaminants suggest that the biomagnification of D5 is being governed by species-specific properties such as biotransformation rate or tissue distribution that differ from those of legacy contaminants.

  13. Floods, Food Webs, and Fluxes in a Northern California channel network

    NASA Astrophysics Data System (ADS)

    Power, M. E.; Dietrich, W. E.; Hondzo, M.; Finlay, J. C.; McNeely, C.; Schade, J.; Welter, J.; Limm, M.; Bode, C.

    2005-05-01

    Following flood scour, re-assembling river food webs respond to solute and particle fluxes. During periods of relatively low flow and high biomass, food webs will also intercept and alter these fluxes. We are studying these interactions in the South Fork Eel River and its tributaries in northern California, a steep drainage system subject to a Mediterranean climate regime. During the biologically productive summer low flow season, large algal blooms in sunlit channels tend to follow bed scouring winter floods. These blooms have strong impacts on consumers and predators in local food webs, and on local fluxes, including cross-habitat food web exchange mediated by insect emergence. We are just beginning to study the effects of blooms on fluxes through channels over larger spatial and temporal scales. Year-to-year variation in the magnitude of algal blooms will produce corresponding variation in pulsed releases of organic matter, stored temporarily in the beds of deep pools, and ultimately, in this incised system, in off shore ocean sediments. A small but ecologically significant component, however, may be stored as biomass in long lived vertebrate predators, including bats and salmonids. The ultimate goal of quantifying relationships among flow regimes, ecosystem productivity, food web responses, and fluxes through watersheds will require prolonged cross-disciplinary collaborations, but may become increasingly feasible due to access to new sensor, tracing and mapping technologies.

  14. Internet food marketing strategies aimed at children and adolescents: a content analysis of food and beverage brand web sites.

    PubMed

    Weber, Kristi; Story, Mary; Harnack, Lisa

    2006-09-01

    Americans are spending an increasing amount of time using "new media" like the Internet. There has been little research examining food and beverage Web sites' content and marketing practices, especially those that attract children and adolescents. The purpose of this study was to conduct a content analysis of food- and beverage-brand Web sites and the marketing techniques and advertising strategies present on these sites. The top five brands in eight food and beverage categories, 40 brands in total, were selected based on annual sales data from Brandweek magazine's annual "Superbrands" report. Data were collected using a standardized coding form. The results show a wide variety of Internet marketing techniques and advertising strategies targeting children and adolescents. "Advergaming" (games in which the advertised product is part of the game) was present on 63% of the Web sites. Half or more of the Web sites used cartoon characters (50%) or spokescharacters (55%), or had a specially designated children's area (58%) with a direct link from the homepage. With interactive media still in its developmental stage, there is a need to develop safeguards for children. Food and nutrition professionals need to advocate for responsible marketing techniques that will support the health of children.

  15. Is benthic food web structure related to diversity of marine macrobenthic communities?

    NASA Astrophysics Data System (ADS)

    Sokołowski, A.; Wołowicz, M.; Asmus, H.; Asmus, R.; Carlier, A.; Gasiunaité, Z.; Grémare, A.; Hummel, H.; Lesutiené, J.; Razinkovas, A.; Renaud, P. E.; Richard, P.; Kędra, M.

    2012-08-01

    Numerical structure and the organisation of food webs within macrozoobenthic communities has been assessed in the European waters (Svalbard, Barents Sea, Baltic Sea, North Sea, Atlantic Ocean and the Mediterranean Sea) to address the interactions between biodiversity and ecosystem functioning. Abundance and classical species diversity indices (S, H', J) of macrofaunal communities were related to principal attributes of food webs (relative trophic level and food chain length, FCL) that were determined from carbon and nitrogen stable isotope values. Structure of marine macrobenthos varies substantially at a geographical scale; total abundance ranges from 63 ind. m-2 to 34,517 ind. m-2, species richness varies from 3 to 166 and the Shannon-Weaver diversity index from 0.26 to 3.26 while Pielou's evenness index is below 0.73. The major source of energy for macrobenthic communities is suspended particulate organic matter, consisting of phytoplankton and detrital particles, sediment particulate organic matter, and microphytobenthos in varying proportions. These food sources support the presence of suspension- and deposit-feeding communities, which dominate numerically on the sea floor. Benthic food webs include usually four to five trophic levels (FCL varies from 3.08 to 4.86). Most species are assigned to the second trophic level (primary consumers), fewer species are grouped in the third trophic level (secondary consumers), and benthic top predators are the least numerous. Most species cluster primarily at the lowest trophic level that is consistent with the typical organization of pyramidal food webs. Food chain length increases with biodiversity, highlighting a positive effect of more complex community structure on food web organisation. In more diverse benthic communities, energy is transferred through more trophic levels while species-poor communities sustain a shorter food chain.

  16. Climate change impacts on food system

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Cai, X.; Zhu, T.

    2014-12-01

    Food system includes biophysical factors (climate, land and water), human environments (production technologies and food consumption, distribution and marketing), as well as the dynamic interactions within them. Climate change affects agriculture and food systems in various ways. Agricultural production can be influenced directly by climatic factors such as mean temperature rising, change in rainfall patterns, and more frequent extreme events. Eventually, climate change could cause shift of arable land, alteration of water availability, abnormal fluctuation of food prices, and increase of people at risk of malnutrition. This work aims to evaluate how climate change would affect agricultural production biophysically and how these effects would propagate to social factors at the global level. In order to model the complex interactions between the natural and social components, a Global Optimization model of Agricultural Land and Water resources (GOALW) is applied to the analysis. GOALW includes various demands of human society (food, feed, other), explicit production module, and irrigation water availability constraint. The objective of GOALW is to maximize global social welfare (consumers' surplus and producers' surplus).Crop-wise irrigation water use in different regions around the world are determined by the model; marginal value of water (MVW) can be obtained from the model, which implies how much additional welfare benefit could be gained with one unit increase in local water availability. Using GOALW, we will analyze two questions in this presentation: 1) how climate change will alter irrigation requirements and how the social system would buffer that by price/demand adjustment; 2) how will the MVW be affected by climate change and what are the controlling factors. These results facilitate meaningful insights for investment and adaptation strategies in sustaining world's food security under climate change.

  17. Sea lamprey carcasses exert local and variable food web effects in a nutrient-limited Atlantic coastal stream

    USGS Publications Warehouse

    Weaver, Daniel M.; Coghlan Jr., Stephen M.; Zydlewski, Joseph

    2016-01-01

    Resource flows from adjacent ecosystems are critical in maintaining structure and function of freshwater food webs. Migrating sea lamprey (Petromyzon marinus) deliver a pulsed marine-derived nutrient subsidy to rivers in spring when the metabolic demand of producers and consumers are increasing. However, the spatial and temporal dynamics of these nutrient subsidies are not well characterized. We used sea lamprey carcass additions in a small stream to examine changes in nutrients, primary productivity, and nutrient assimilation among consumers. Algal biomass increased 57%–71% immediately adjacent to carcasses; however, broader spatial changes from multiple-site carcass addition may have been influenced by canopy cover. We detected assimilation of nutrients (via δ13C and δ15N) among several macroinvertebrate families including Heptageniidae, Hydropsychidae, and Perlidae. Our research suggests that subsidies may evoke localized patch-scale effects on food webs, and the pathways of assimilation in streams are likely coupled to adjacent terrestrial systems. This research underscores the importance of connectivity in streams, which may influence sea lamprey spawning and elicit varying food web responses from carcass subsidies due to fine-scale habitat variables.

  18. Reconciling the role of organic matter pathways in aquatic food webs by measuring multiple tracers in individuals.

    PubMed

    Jardine, Timothy D; Woods, Ryan; Marshall, Jonathan; Fawcetr, James; Lobegeiger, Jaye; Valdez, Dominic; Kainz, Martin J

    2015-12-01

    Few studies measure multiple ecological tracers in individual organisms, thus limiting our ability to differentiate among organic matter source pathways and understand consequences of dietary variation and the use of external subsidies in complex food webs. We combined two tracers, stable isotope (SI) ratios and fatty acids (FA), to investigate linkages among ecological compartments (water column, benthos, riparian zone) in food webs in waterholes of a dryland river network, the Border Rivers in southwestern Queensland, Australia. Comprehensive analyses of sources (plankton, periphyton, leaf litter, riparian grasses) and animals (benthic insects, mollusks, large crustaceans, fishes) for SI and FA showed that all three zones contribute to animal biomass, depending on species and life stage. Large fishes derived a subsidy from the riparian/floodplain zone, likely through the consumption of terrestrial and semi-aquatic insects and prawns that fed on detritivorous insects. Importantly, post-larval bony bream (Nematalosa erebi) and golden perch (Macquaria ambigua) were tightly connected to the water column, as evidenced by 13C-depleted, 15N-enriched isotope ratios and a high content of plankton-derived polyunsaturated fatty acids (eicosapentaenoic acid [EPA; 20:53] and docosahexaenoic acid [DHA; 22:6003]). These observations were consistent with expectations from nutritional requirements of fish early life stages and habitat changes associated with maturity. These results highlight the importance of high-quality foods during early development of fishes, and show that attempting to attribute food-web production to a single source pathway overlooks important but often subtle subsidies that maintain viable populations. A complete understanding of food-web dynamics must consider both quantity and quality of different available organic matter sources. This understanding can be achieved with a combined SI and FA approach, but more controlled dietary studies are needed to

  19. Evaluating the effects of trophic complexity on a keystone predator by disassembling a partial intraguild predation food web.

    PubMed

    Davenport, Jon M; Chalcraft, David R

    2012-01-01

    1. Many taxa can be found in food webs that differ in trophic complexity, but it is unclear how trophic complexity affects the performance of particular taxa. In pond food webs, larvae of the salamander Ambystoma opacum occupy the intermediate predator trophic position in a partial intraguild predation (IGP) food web and can function as keystone predators. Larval A. opacum are also found in simpler food webs lacking either top predators or shared prey. 2. We conducted an experiment where a partial IGP food web was simplified, and we measured the growth and survival of larval A. opacum in each set of food webs. Partial IGP food webs that had either a low abundance or high abundance of total prey were also simplified by independently removing top predators and/or shared prey. 3. Removing top predators always increased A. opacum survival, but removal of shared prey had no effect on A. opacum survival, regardless of total prey abundance. 4. Surprisingly, food web simplification had no effect on the growth of A. opacum when present in food webs with a low abundance of prey but had important effects on A. opacum growth in food webs with a high abundance of prey. Simplifying a partial IGP food web with a high abundance of prey reduced A. opacum growth when either top predators or shared prey were removed from the food web and the loss of top predators and shared prey influenced A. opacum growth in a non-additive fashion. 5. The non-additive response in A. opacum growth appears to be the result of supplemental prey availability augmenting the beneficial effects of top predators. Top predators had a beneficial effect on A. opacum populations by reducing the abundance of A. opacum present and thereby reducing the intensity of intraspecific competition. 6. Our study indicates that the effects of food web simplification on the performance of A. opacum are complex and depend on both how a partial IGP food web is simplified and how abundant prey are in the food web. These

  20. Medium-sized exotic prey create novel food webs: the case of predators and scavengers consuming lagomorphs

    PubMed Central

    Hiraldo, Fernando; Lambertucci, Sergio A.

    2016-01-01

    Food web interactions are key to community structure. The introduction of species can be seen as an uncontrolled experiment of the addition of species. Introduced species lead to multiple changes, frequently threatening the native biodiversity. However, little is known about their direct effect on the upper level of the food web. In this study we review empirical data on the predator–prey relationship between the introduced lagomorphs and their consumers, and use meta-analytical tools to quantify the strength of their interactions. We expect that exotic lagomorphs will destabilize food webs, affect ecological processes and compromise the conservation of the invaded regions. We found 156 studies on the diet of 43 species of predators that consume lagomorphs as exotic preys in South America and Oceania. We found an average exotic lagomorphs-predator link of 20% which indicates a strong interaction, given that the average for the strongest links with native prey (when lagomorphs are not included in the predator diet) is about 24%. Additionally, this last link decreases to 17% when lagomorphs are present. When lagomorphs arrive in a new environment they may become the most important resource for predators, producing an unstable equilibrium in the novel food web. Any disruption of this interaction could have catastrophic consequences for the native diversity by directly impacting predators or indirectly impacting native preys by apparent competition. Eradication or any change in their abundances should be carefully considered in conservation actions since those will have great impacts on predator populations and ultimately in the whole communities. PMID:27547575

  1. Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.

    PubMed

    Surma, Szymon; Pakhomov, Evgeny A; Pitcher, Tony J

    2014-01-01

    The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

  2. Distributions of key exposure factors controlling the uptake of xenobiotic chemicals in an estuarine food web

    SciTech Connect

    Iannuzzi, T.J.; Harrington, N.W.; Shear, N.M.; Curry, C.L.; Carlson-Lynch, H.; Henning, M.H.; Su, S.H.; Rabbe, D.E.

    1996-11-01

    A critical evaluation of literature on the behavior, physiology, and ecology of common estuarine organisms was conducted in an attempt to develop probabilistic distributions for those variables that influence the uptake of xenobiotic chemicals from sediments, water, and food sources. The ranges, central tendencies, and distributions of several key parameter values were identified for dominant organisms from various trophic levels, including the polychaete Nereis virens, mummichog (Fundulus heteroclitus), blue crab (Callinectes sapidus), and striped bass (Morone saxatilis). The exposure factors of interest included ingestion rate for various food sources, growth rate, respiration rate, excretion rate, body weight, wet/dry weight ratio, lipid content, chemical assimilation efficiency, and food assimilation efficiency. These exposure factors are critical to the execution of mechanistic food web models, which, when properly calibrated, can be used to estimate tissue concentrations of nonionic chemicals in aquatic organisms based on knowledge of the bioenergetics and feeding interactions within a food web and the sediment and water concentrations of chemicals. In this article the authors describe the use of distributions for various exposure factors in the context of a mechanistic bioaccumulation model that is amenable to probabilistic analyses for multiple organisms within a food web. A case study is provided which compares the estimated versus measured concentrations of five polychlorinated biphenyl (PCB) congeners in a representative food web from the tidal portion of the Passaic River, New Jersey, USA. The results suggest that the model is accurate within an order of magnitude or less in estimating the bioaccumulation of PCBs in this food web without calibration. The results of a model sensitivity analysis suggest that the input parameters which most influence the output of the model are both chemical and organism specific.

  3. The rapid return of marine-derived nutrients to a freshwater food web following dam removal

    USGS Publications Warehouse

    Tonra, Christopher M; Sager-Fradkin, Kimberly A.; Morley, Sarah A; Duda, Jeff; Marra, Peter P.

    2015-01-01

    Dam removal is increasingly being recognized as a viable river restoration action. Although the main beneficiaries of restored connectivity are often migratory fish populations, little is known regarding recovery of other parts of the freshwater food web, particularly terrestrial components. We measured stable isotopes in key components to the freshwater food web: salmon, freshwater macroinvertebrates and a river specialist bird, American dipper (Cinclus mexicanus), before and after removal of the Elwha Dam, WA, USA. Less than a year after dam removal, salmon returned to the system and released marine-derived nutrients (MDN). In that same year we documented an increase in stable-nitrogen and carbon isotope ratios in American dippers. These results indicate that MDN from anadromous fish, an important nutrient subsidy that crosses the aquatic–terrestrial boundary, can return rapidly to food webs after dams are removed which is an important component of ecosystem recovery.

  4. More than a meal: integrating non-feeding interactions into food webs

    USGS Publications Warehouse

    Kéfi, Sonia; Berlow, Eric L.; Wieters, Evie A.; Navarrete, Sergio A.; Petchey, Owen L.; Wood, Spencer A.; Boit, Alice; Joppa, Lucas N.; Lafferty, Kevin D.; Williams, Richard J.; Martinez, Neo D.; Menge, Bruce A.; Blanchette, Carol A.; Iles, Alison C.; Brose, Ulrich

    2012-01-01

    Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature.

  5. Food webs are more than the sum of their tritrophic parts

    PubMed Central

    Cohen, Joel E.; Schittler, Daniella N.; Raffaelli, David G.; Reuman, Daniel C.

    2009-01-01

    Many studies have aimed to understand food webs by investigating components such as trophic links (one consumer taxon eats one resource taxon), tritrophic interactions (one consumer eats an intermediate taxon, which eats a resource), or longer chains of links. We show here that none of these components (links, tritrophic interactions, and longer chains), individually or as an ensemble, accounts fully for the properties of the next higher level of organization. As a cell is more than its molecules, as an organ is more than its cells, and as an organism is more than its organs, in a food web, new structure emerges at every organizational level up to and including the whole web. We demonstrate the emergence of properties at progressively higher levels of structure by using all of the directly observed, appropriately organized, publicly available food web datasets with relatively complete trophic link data and with average body mass and population density data for each taxon. There are only three such webs, those of Tuesday Lake, Michigan, in 1984 and 1986, and Ythan Estuary, Scotland. We make the data freely available online with this report. Differences in web patterns between Tuesday Lake and Ythan Estuary, and similarities of Tuesday Lake in 1984 and 1986 despite 50% turnover of species, suggest that the patterns we describe respond to major differences between ecosystem types. PMID:20018774

  6. Food security in a changing climate

    USGS Publications Warehouse

    Pulwarty, Roger; Eilerts, Gary; Verdin, James

    2012-01-01

    By 2080 the effects of climate change—on heat waves, floods, sea level rise, and drought—could push an additional 600 million people into malnutrition and increase the number of people facing water scarcity by 1.8 billion. The precise impacts will, however, strongly depend on socioeconomic conditions such as local markets and food import dependence. In the near term, two factors are also changing the nature of food security: (1) rapid urbanization, with the proportion of the global population living in urban areas expanding from 13 percent in 1975 to greater than 50 percent at present, and (2) trade and domestic market liberalization since 1993, which has promoted removal of import controls, deregulation of prices, and the loss of preferential markets for many small economies. Over the last two years, the worst drought in decades has devastated eastern Africa. The resulting food-security crisis has affected roughly 13 million people and has reminded us that there is still a long way to go in addressing current climate-related risks. In the face of such profound changes and uncertainties, our approaches to food security must evolve. In this article, we describe four key elements that, in our view, will be essential to the success of efforts to address the linked challenges of food security and climate change.

  7. US Food and Drug Administration Web Site: A Primer for Pharmacists

    PubMed Central

    Baker, Danial E.

    2015-01-01

    The US Food and Drug Administration (FDA) Web site includes a vast amount of information, but it can be difficult to navigate. Despite frequently asked question (FAQ)–type pages within the Web site, it may not be easy for first-time users to find drug information. This article presents some examples of common questions, provides the locations of the answers on the FDA Web site, and gives a brief description of some of the many resources the FDA provides for health care professionals. Additionally, a newer project being undertaken by the FDA, Snapshot, is introduced. PMID:27621506

  8. US Food and Drug Administration Web Site: A Primer for Pharmacists.

    PubMed

    Leonard, James; Baker, Danial E

    2015-11-01

    The US Food and Drug Administration (FDA) Web site includes a vast amount of information, but it can be difficult to navigate. Despite frequently asked question (FAQ)-type pages within the Web site, it may not be easy for first-time users to find drug information. This article presents some examples of common questions, provides the locations of the answers on the FDA Web site, and gives a brief description of some of the many resources the FDA provides for health care professionals. Additionally, a newer project being undertaken by the FDA, Snapshot, is introduced.

  9. Impacts of food web structure and feeding behavior on mercury exposure in Greenland Sharks (Somniosus microcephalus).

    PubMed

    McMeans, Bailey C; Arts, Michael T; Fisk, Aaron T

    2015-03-15

    Benthic and pelagic food web components in Cumberland Sound, Canada were explored as sources of total mercury (THg) to Greenland Sharks (Somniosus microcephalus) via both bottom-up food web transfer and top-down shark feeding behavior. Log10THg increased significantly with δ(15)N and trophic position from invertebrates (0.01 ± 0.01 μg · g(-1) [113 ± 1 ng · g(-1)] dw in copepods) to Greenland Sharks (3.54 ± 1.02 μg · g(-1)). The slope of the log10THg vs. δ(15)N linear regression was higher for pelagic compared to benthic food web components (excluding Greenland Sharks, which could not be assigned to either food web), which resulted from THg concentrations being higher at the base of the benthic food web (i.e., in benthic than pelagic primary consumers). However, feeding habitat is unlikely to consistently influence shark THg exposure in Cumberland Sound because THg concentrations did not consistently differ between benthic and pelagic shark prey. Further, size, gender and feeding behavior (inferred from stable isotopes and fatty acids) were unable to significantly explain THg variability among individual Greenland Sharks. Possible reasons for this result include: 1) individual sharks feeding as generalists, 2) high overlap in THg among shark prey, and 3) differences in turnover time between ecological tracers and THg. This first assessment of Greenland Shark THg within an Arctic food web revealed high concentrations consistent with biomagnification, but low ability to explain intra-specific THg variability. Our findings of high THg levels and consumption of multiple prey types, however, suggest that Greenland Sharks acquire THg through a variety of trophic pathways and are a significant contributor to the total biotic THg pool in northern seas.

  10. Synthesis: comparing effects of resource and consumer fluxes into recipient food webs using meta-analysis.

    PubMed

    Allen, Daniel C; Wesner, Jeff S

    2016-03-01

    Here we synthesize empirical research using meta-analysis to compare how consumer and resource fluxes affect recipient food webs. We tested the following hypotheses: (H1) The direct effects of resource fluxes (bottom-up) should be stronger than the direct effects of consumer fluxes (top-down), because resource fluxes are permanent (do not return to the food web in which they were produced) but consumer fluxes may not be (consumers can leave). (H2) Following H1, the indirect effects should attenuate (weaken) more quickly for consumer fluxes than for resource fluxes due to their direct effects being weaker, (H3) The effects of resource fluxes should be stronger when recipient food webs are in different ecosystems than donor food webs due to differences in elevation that accompany cross-ecosystem food web interfaces, often increasing flux quantity due to gravity, while the effects of consumer fluxes should be stronger when donor and recipient food webs are in the same ecosystem as they should more easily assimilate into the recipient food web. We found no differences in the magnitude of bottom-up and top-down direct effects for resource and consumer fluxes, but top-down direct effects were 122% stronger than top-down indirect effects. Indirect effects of prey and predator fluxes quickly attenuated while indirect effects of non-prey resource and herbivore fluxes did not, as the overall direct effects of prey and predator fluxes were 123% and 163% stronger than their indirect effects, respectively. This result suggests that the magnitude of indirect effects decrease as the trophic level of resource and consumer fluxes increases, and also contrasts with results from studies showing in situ top-down indirect effects are stronger than in situ bottom-up indirect effects. We found that resource and consumer flux effect sizes were similar when they occurred between ecosystems, but when they occurred within ecosystems predator flux effects were 107% stronger than nutrient flux

  11. Taking the trophic bypass: aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web.

    PubMed

    Bartrons, Mireia; Gratton, Claudio; Spiesman, Brian J; Vander Zanden, M Jake

    2015-01-01

    Ecosystems can be linked by the movement of matter and nutrients across habitat boundaries via aquatic insect emergence. Aquatic organisms tend to have higher concentrations of certain toxic contaminants such as methylmercury (MeHg) compared to their terrestrial counterparts. If aquatic organisms come to land, terrestrial organisms that consume them are expected to have elevated MeHg concentrations. But emergent aquatic insects could have other impacts as well, such as altering consumer trophic position or increasing ecosystem productivity as a result of nutrient inputs from insect carcasses. We measure MeHg in terrestrial arthropods at two lakes in northeastern Iceland and use carbon and nitrogen stable isotopes to quantify aquatic reliance and trophic position. Across all terrestrial focal arthropod taxa (Lycosidae, Linyphiidae, Acari, Opiliones), aquatic reliance had significant direct and indirect (via changes in trophic position) effects on terrestrial consumer MeHg. However, contrary to our expectations, terrestrial consumers that consumed aquatic prey had lower MeHg concentrations than consumers that ate mostly terrestrial prey. We hypothesize that this is due to the lower trophic position of consumers feeding directly on midges relative to those that fed mostly on terrestrial prey and that had, on average, higher trophic positions. Thus, direct consumption of aquatic inputs results in a trophic bypass that creates a shorter terrestrial food web and reduced biomagnification of MeHg across the food web. Our finding that MeHg was lower at terrestrial sites with aquatic inputs runs counter to the conventional wisdom that aquatic systems are a source of MeHg contamination to surrounding terrestrial ecosystems.

  12. Major constrains of the pelagic food web efficiency in the Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Zoccarato, L.; Fonda Umani, S.

    2015-03-01

    Grazing pressure plays a key role on plankton communities affecting their biodiversity and shaping their structures. Predation exerted by 2-200 μm protists (i.e. microzooplankton and heterotrophic nanoplankton) influences the carbon fate in marine environments channeling new organic matter from the microbial loop toward the "classic" grazing food web. In this study, we analyzed more than 80 dilution experiments carried out in many Mediterranean sites at the surface and in the meso-bathypelagic layers. Our aims were to investigate prey-predator interactions and determine selectivity among energy sources (in terms of available biomass), efficiency in the exploitation and highlight likely constrains that can modulate carbon transfer processes within the pelagic food webs. Generally, microzooplankton shown higher impacts on prey stocks than heterotrophic nanoflagellates, expressing larger ingestion rates and efficiency. Through different trophic conditions characterized on the base of chlorophyll a concentration, microzooplankton diet has shown to change in prey compositions: nano- and picoplankton almost completely covered consumer needs in oligotrophy and mesotrophy, while microphytoplankton (mostly diatoms) represented more than 80% of the consumers' diet in eutrophy, where, nevertheless, picoplankton mortality remained relatively high. Ingestion rates of both consumers (nano- and microzooplankters) increased with the availability of prey biomasses and consequently with the trophic condition of the environment. Nevertheless, overall the heterotrophic fraction of picoplankton resulted the most exploited biomass by both classes of consumers. Ingestion efficiency (as the ratio between available biomass and ingestion rate) increased at low biomasses and therefore the highest efficiencies were recorded in oligotrophic conditions and in the bathypelagic layers.

  13. Biodilution of heavy metals in a stream macroinvertebrate food web: evidence from stable isotope analysis.

    PubMed

    Watanabe, Kozo; Monaghan, Michael T; Takemon, Yasuhiro; Omura, Tatsuo

    2008-05-01

    Analysis of carbon (delta13C) and nitrogen (delta15N) stable isotopes provides an increasingly important means of understanding the complex trophic structure of macroinvertebrate communities in streams. We coupled a stable isotope approach with a contaminant analysis of six metals (Pb, Ag, Zn, Hg, Cu, As) to trace the accumulation and dilution of metals from an abandoned mine across trophic levels of the benthic community in Ginzan Creek, Japan. The delta15N signature increased with trophic level, with mean increases of 4.70 per thousand from producers to primary consumers and 3.06 per thousand from primary to secondary consumers. Tissue Pb and Ag concentrations were negatively correlated with delta15N, indicating biodilution of both metals through the food web. Although macroinvertebrate taxon body mass was negatively correlated with tissue metal concentration at several sites, it did not increase with trophic level (as delta15N) in any of the sites, suggesting that changes in body mass were not the cause of biodilution. Our findings suggest invertebrates at higher trophic levels may exhibit increasingly efficient excretion of metals. Autotrophic epilithon (mean delta13C= -21.3 per thousand) had a much higher concentration of mined metals than did riparian vegetation (mean delta13C= -29.3 per thousand); nonetheless, a carbon-mixing model indicated that taxa feeding on autochthonous carbon sources did not accumulate more metal than allochthonous feeders. It is likely that the notably high metal concentration of allochthonous FPOM plays an important role in the trophic transfer of metals. Our data suggest the strong potential for stable isotope analysis to enhance our understanding of metal transfer through stream macroinvertebrate food webs.

  14. Reciprocal diversification in a complex plant-herbivore-parasitoid food web

    PubMed Central

    Nyman, Tommi; Bokma, Folmer; Kopelke, Jens-Peter

    2007-01-01

    Background Plants, plant-feeding insects, and insect parasitoids form some of the most complex and species-rich food webs. According to the classic escape-and-radiate (EAR) hypothesis, these hyperdiverse communities result from coevolutionary arms races consisting of successive cycles of enemy escape, radiation, and colonization by new enemy lineages. It has also been suggested that "enemy-free space" provided by novel host plants could promote host shifts by herbivores, and that parasitoids could similarly drive diversification of gall form in insects that induce galls on plants. Because these central coevolutionary hypotheses have never been tested in a phylogenetic framework, we combined phylogenetic information on willow-galling sawflies with data on their host plants, gall types, and enemy communities. Results We found that evolutionary shifts in host plant use and habitat have led to dramatic prunings of parasitoid communities, and that changes in gall phenotype can provide "enemy-free morphospace" for millions of years even in the absence of host plant shifts. Some parasites have nevertheless managed to colonize recently-evolved gall types, and this has apparently led to adaptive speciation in several enemy groups. However, having fewer enemies does not in itself increase speciation probabilities in individual sawfly lineages, partly because the high diversity of the enemy community facilitates compensatory attack by remaining parasite taxa. Conclusion Taken together, our results indicate that niche-dependent parasitism is a major force promoting ecological divergence in herbivorous insects, and that prey divergence can cause speciation in parasite lineages. However, the results also show that the EAR hypothesis is too simplistic for species-rich food webs: instead, diversification seems to be spurred by a continuous stepwise process, in which ecological and phenotypic shifts in prey lineages are followed by a lagged evolutionary response by some of the

  15. Climate change - Agricultural land use - Food security

    NASA Astrophysics Data System (ADS)

    Nagy, János; Széles, Adrienn

    2015-04-01

    In Hungary, plougland decreased to 52% of its area by the time of political restructuring (1989) in comparison with the 1950s. Forested areas increased significantly (18%) and lands withdrawn from agricultural production doubled (11%). For today, these proportions further changed. Ploughlands reduced to 46% and forested areas further increased (21%) in 2013. The most significat changes were observed in the proportion of lands withdrawn from agricultural production which increased to 21%. Temperature in Hungary increased by 1°C during the last century and predictions show a further 2.6 °C increase by 2050. The yearly amount of precipitation significantly decreased from 640 mm to 560 mm with a more uneven temporal distribution. The following aspects can be considered in the correlation between climate change and agriculture: a) impact of agriculture on climate, b) future impact of climate change on agriculture and food supply, c) impact of climate change on food security. The reason for the significant change of climate is the accumulation of greenhouse gases (GHG) which results from anthropological activities. Between 2008 and 2012, Hungary had to reduce its GHG emission by 6% compared to the base period between 1985-1987. At the end of 2011, Hungarian GHG emission was 43.1% lower than that of the base period. The total gross emission was 66.2 million CO2 equivalent, while the net emission which also includes land use, land use change and forestry was 62.8 million tons. The emission of agriculture was 8.8 million tons (OMSZ, 2013). The greatest opportunity to reduce agricultural GHG emission is dinitrogen oxides which can be significantly mitigated by the smaller extent and more efficient use of nitrogen-based fertilisers (precision farming) and by using biomanures produced from utilised waste materials. Plant and animal species which better adapt to extreme weather circumstances should be bred and maintained, thereby making an investment in food security. Climate

  16. Warming effects on marine microbial food web processes: how far can we go when it comes to predictions?

    PubMed

    Sarmento, Hugo; Montoya, José M; Vázquez-Domínguez, Evaristo; Vaqué, Dolors; Gasol, Josep M

    2010-07-12

    Previsions of a warmer ocean as a consequence of climatic change point to a 2-6 degrees C temperature rise during this century in surface oceanic waters. Heterotrophic bacteria occupy the central position of the marine microbial food web, and their metabolic activity and interactions with other compartments within the web are regulated by temperature. In particular, key ecosystem processes like bacterial production (BP), respiration (BR), growth efficiency and bacterial-grazer trophic interactions are likely to change in a warmer ocean. Different approaches can be used to predict these changes. Here we combine evidence of the effects of temperature on these processes and interactions coming from laboratory experiments, space-for-time substitutions, long-term data from microbial observatories and theoretical predictions. Some of the evidence we gathered shows opposite trends to warming depending on the spatio-temporal scale of observation, and the complexity of the system under study. In particular, we show that warming (i) increases BR, (ii) increases bacterial losses to their grazers, and thus bacterial-grazer biomass flux within the microbial food web, (iii) increases BP if enough resources are available (as labile organic matter derived from phytoplankton excretion or lysis), and (iv) increases bacterial losses to grazing at lower rates than BP, and hence decreasing the proportion of production removed by grazers. As a consequence, bacterial abundance would also increase and reinforce the already dominant role of microbes in the carbon cycle of a warmer ocean.

  17. Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study

    USGS Publications Warehouse

    Stewart, A.R.; Luoma, S.N.; Schlekat, C.E.; Doblin, M.A.; Hieb, K.A.

    2004-01-01

    Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean Zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, ke = 0.025, 0.155, and 0.25 d-1, respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se > 15 ??g g-1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of Zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.

  18. Warming shifts top-down and bottom-up control of pond food web structure and function.

    PubMed

    Shurin, Jonathan B; Clasen, Jessica L; Greig, Hamish S; Kratina, Pavel; Thompson, Patrick L

    2012-11-05

    The effects of global and local environmental changes are transmitted through networks of interacting organisms to shape the structure of communities and the dynamics of ecosystems. We tested the impact of elevated temperature on the top-down and bottom-up forces structuring experimental freshwater pond food webs in western Canada over 16 months. Experimental warming was crossed with treatments manipulating the presence of planktivorous fish and eutrophication through enhanced nutrient supply. We found that higher temperatures produced top-heavy food webs with lower biomass of benthic and pelagic producers, equivalent biomass of zooplankton, zoobenthos and pelagic bacteria, and more pelagic viruses. Eutrophication increased the biomass of all organisms studied, while fish had cascading positive effects on periphyton, phytoplankton and bacteria, and reduced biomass of invertebrates. Surprisingly, virus biomass was reduced in the presence of fish, suggesting the possibility for complex mechanisms of top-down control of the lytic cycle. Warming reduced the effects of eutrophication on periphyton, and magnified the already strong effects of fish on phytoplankton and bacteria. Warming, fish and nutrients all increased whole-system rates of net production despite their distinct impacts on the distribution of biomass between producers and consumers, plankton and benthos, and microbes and macrobes. Our results indicate that warming exerts a host of indirect effects on aquatic food webs mediated through shifts in the magnitudes of top-down and bottom-up forcing.

  19. Ecosystem consequences of species richness and composition in pond food webs.

    PubMed

    Downing, Amy L; Leibold, Mathew A

    2002-04-25

    Resolving current concerns about the role of biodiversity on ecosystems calls for understanding the separate roles of changes in species numbers and of composition. Recent work shows that primary productivity often, but not always, saturates with species richness within single trophic levels. However, any interpretation of such patterns must consider that variation in biodiversity is necessarily associated with changes in species composition (identity), and that changes in biodiversity often occur across multiple trophic levels. Here we present results from a mesocosm experiment in which we independently manipulated species richness and species composition across multiple trophic levels in pond food webs. In contrast to previous studies that focused on single trophic levels, we found that productivity is either idiosyncratic or increases with respect to species richness, and that richness influences trophic structure. However, the composition of species within richness levels can have equally or more marked effects on ecosystems than average effects of richness per se. Indirect evidence suggests that richness and associated changes in species composition affect ecosystem attributes through indirect effects and trophic interactions among species, features that are highly characteristic of natural, complex ecosystems.

  20. Variable and complex food web structures revealed by exploring missing trophic links between birds and biofilm.

    PubMed

    Kuwae, Tomohiro; Miyoshi, Eiichi; Hosokawa, Shinya; Ichimi, Kazuhiko; Hosoya, Jun; Amano, Tatsuya; Moriya, Toshifumi; Kondoh, Michio; Ydenberg, Ronald C; Elner, Robert W

    2012-04-01

    Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical and variable, by revealing that direct predator-prey relationships between shorebirds and biofilm are widespread and mediated by multiple ecological and evolutionary determinants. Food source mixing models and energy budget estimates indicate that the strength of the missing linkage is dependent on predator traits (body mass and foraging action rate) and the environment that determines food density. Morphological analyses, showing that smaller bodied species possess more developed feeding apparatus to consume biofilm, suggest that the linkage is also phylogenetically dependent and affords a compelling re-interpretation of niche differentiation. We contend that exploring missing links is a necessity for revealing true network structure and dynamics.

  1. Effects of genetically modified maize events expressing Cry34Ab1, Cry35Ab1, Cry1F, and CP4 EPSPS proteins on arthropod complex food webs.

    PubMed

    Pálinkás, Zoltán; Kiss, József; Zalai, Mihály; Szénási, Ágnes; Dorner, Zita; North, Samuel; Woodward, Guy; Balog, Adalbert

    2017-04-01

    Four genetically modified (GM) maize (Zea mays L.) hybrids (coleopteran resistant, coleopteran and lepidopteran resistant, lepidopteran resistant and herbicide tolerant, coleopteran and herbicide tolerant) and its non-GM control maize stands were tested to compare the functional diversity of arthropods and to determine whether genetic modifications alter the structure of arthropods food webs. A total number of 399,239 arthropod individuals were used for analyses. The trophic groups' number and the links between them indicated that neither the higher magnitude of Bt toxins (included resistance against insect, and against both insects and glyphosate) nor the extra glyphosate treatment changed the structure of food webs. However, differences in the average trophic links/trophic groups were detected between GM and non-GM food webs for herbivore groups and plants. Also, differences in characteristic path lengths between GM and non-GM food webs for herbivores were observed. Food webs parameterized based on 2-year in-field assessments, and their properties can be considered a useful and simple tool to evaluate the effects of Bt toxins on non-target organisms.

  2. Pollution-induced community tolerance and functional redundancy in a decomposer food web in metal-stressed soil.

    PubMed

    Salminen, J; van Gestel, C A; Oksanen, J

    2001-10-01

    Pollution may lead to the development of pollution-induced community tolerance (PICT) in a stressed community. We studied the presence of PICT in soil food webs using soil microcosms. Soil microcosms containing soil invertebrates and microbes were collected from polluted and unpolluted areas and exposed to a range of soil zinc concentrations. A pine seedling was planted in each microcosm to measure the effects of the origin of the community and Zn pollution on above-ground plant production. The effects of the treatments on nutrient content in the soil were also measured. The diversity of soil microarthropods and the soil's mineral nutrient content were low at the Zn-polluted site. We did not observe an increasing Zn tolerance among the soil organisms in the polluted soil. However, low population growth rates of soil invertebrates from the polluted site may indicate the deleterious effects on fitness of long-lasting pollution. In the soil from the nonpolluted site, Zn additions caused changes in the invertebrate food web structure. These changes were explained by the good physiological condition of the animals and their insensitivity to Zn. The fact that the food web structure in soil from the polluted site did not change can be used as a rough indicator of PICT. Structural stability is presumed by the lack of Zn-sensitive species at this site and the inability of populations to acclimate by altering their growth or reproduction patterns in response to changing soil conditions. Although microbial-based soil decomposer systems may have a high functional redundancy, our results indicate that metal stress at the polluted site exceeds the tolerance limits of the system. As a consequence, ecosystem function at this site is endangered. This study also shows that the evolution of metal tolerance by soil decomposer organisms may not be a common reaction to soil pollution, although changes of population and community structure indicated severe metal stress on organisms.

  3. A preliminary investigation of the fish food web in the Gironde estuary, France, using dietary and stable isotope analyses

    NASA Astrophysics Data System (ADS)

    Pasquaud, S.; Elie, P.; Jeantet, C.; Billy, I.; Martinez, P.; Girardin, M.

    2008-06-01

    Carbon and Nitrogen stable isotopes and stomach contents analyses were used to investigate an estuarine fish food web and identify the contribution of these two methods to the knowledge and understanding of the food web's structure and its functioning. The nine most abundant fish species during the warm period in the Gironde estuary (southwest France, Europe) are examined. Observation of the stomach contents reflects a variety of feeding modes between fish species that consume a diverse assortment of prey, with limited dietary overlap. Nevertheless, when regarding the whole fish community, few prey species dominate the stomach contents. Nitrogen isotope ratios indicate a high intraspecific variability inducing an interspecific covering of the signatures. However, a tendency to δ 15N enrichment according to the trophic position of the species studied was observed. Fish assemblages show a trend towards enrichment of their carbon isotopic signatures from the upper estuary (-20.8 ± 1.8‰) towards the lower estuary (-18.3 ± 1.6‰). But whatever the capture zone considered, most of the individual δ 13C values for each fish analysed are comprised between -22 and -16‰. Only few specimens, belonging to migratory amphihaline species, have significantly lighter values. The stomach contents method of analysis has the advantage of giving an initial view of the ichthyological trophic structure of the system by describing the food relations between a fish species and its prey. From these results, hypotheses can be drawn about the network's functioning, suggesting a sharing of resources between species and a "wasp-waist" control of this estuarine food web. The stable isotope analysis method enables us to improve our structural knowledge by positioning the different species in a food web, with their position being determined by the number of energy transfers (analysis of δ 15N). Conversely, in environments as complex and changing as estuaries, it appears difficult to

  4. Food web of the intertidal rocky shore of the west Portuguese coast - Determined by stable isotope analysis.

    PubMed

    Vinagre, Catarina; Mendonça, Vanessa; Narciso, Luís; Madeira, Carolina

    2015-09-01

    The characterization of food web structure, energy pathways and trophic linkages is essential for the understanding of ecosystem functioning. Isotopic analysis was performed on food web components of the rocky intertidal ecosystem in four sites along the Portuguese west coast. The aim was to 1) determine the general food web structure, 2) estimate the trophic level of the dominant organisms and 3) track the incorporation of organic carbon of different origins in the diet of the top consumers. In this food web, fish are top consumers, followed by shrimp. Anemones and gastropods are intermediate consumers, while bivalves and zooplankton are primary consumers. Macroalgae Bifurcaria bifurcata, Ulva lactuca, Fucus vesiculosus, Codium sp. and phytoplankton are the dominant producers. Two energy pathways were identified, pelagic and benthic. Reliance on the benthic energy pathway was high for many of the consumers but not as high as previously observed in subtidal coastal food webs. The maximum TL was 3.3, which is indicative of a relatively short food web. It is argued that the diet of top consumers relies directly on low levels of the food web to a considerable extent, instead of on intermediate levels, which shortens the trophic length of the food web.

  5. Depth-specific Analyses of the Lake Superior Food Web

    EPA Science Inventory

    Characteristics of large, deep aquatic systems include depth gradients in community composition, in the quality and distribution of food resources, and in the strategies that organisms use to obtain their nutrition. In Lake Superior, nearshore communities that rely upon a combina...

  6. Deforestation-driven food-web collapse linked to emerging tropical infectious disease, Mycobacterium ulcerans

    PubMed Central

    Morris, Aaron L.; Guégan, Jean-François; Andreou, Demetra; Marsollier, Laurent; Carolan, Kevin; Le Croller, Marie; Sanhueza, Daniel; Gozlan, Rodolphe E.

    2016-01-01

    Generalist microorganisms are the agents of many emerging infectious diseases (EIDs), but their natural life cycles are difficult to predict due to the multiplicity of potential hosts and environmental reservoirs. Among 250 known human EIDs, many have been traced to tropical rain forests and specifically freshwater aquatic systems, which act as an interface between microbe-rich sediments or substrates and terrestrial habitats. Along with the rapid urbanization of developing countries, population encroachment, deforestation, and land-use modifications are expected to increase the risk of EID outbreaks. We show that the freshwater food-web collapse driven by land-use change has a nonlinear effect on the abundance of preferential hosts of a generalist bacterial pathogen, Mycobacterium ulcerans. This leads to an increase of the pathogen within systems at certain levels of environmental disturbance. The complex link between aquatic, terrestrial, and EID processes highlights the potential importance of species community composition and structure and species life history traits in disease risk estimation and mapping. Mechanisms such as the one shown here are also central in predicting how human-induced environmental change, for example, deforestation and changes in land use, may drive emergence. PMID:27957534

  7. Interactive effects of chemical and biological controls on food-web composition in saline prairie lakes

    PubMed Central

    2012-01-01

    Salinity is restricting habitatability for many biota in prairie lakes due to limited physiological abilities to cope with increasing osmotic stress. Yet, it remains unclear how salinity effects vary among major taxonomic groups and what role other environmental parameters play in shaping food-web composition. To answer these questions, we sampled fish, zooplankton and littoral macroinvertebrates in 20 prairie lakes (Saskatchewan, Canada) characterized by large gradients in water chemistry and lake morphometry. We showed that salinity thresholds differed among major taxonomic groups, as most fishes were absent above salinities of 2 g L-1, while littoral macroinvertebrates were ubiquitous. Zooplankton occurred over the whole salinity range, but changed taxonomic composition as salinity increased. Subsequently, the complexity of fish community (diversity) was associated with large changes in invertebrate communities. The directional changes in invertebrate communities to smaller taxa indicated that complex fish assemblages resulted in higher predation pressure. Most likely, as the complexity of fish community decreased, controls of invertebrate assemblages shifted from predation to competition and ultimately to productivity in hypersaline lakes. Surprisingly, invertebrate predators did not thrive in the absence of fishes in these systems. Furthermore, the here identified salinity threshold for fishes was too low to be a result of osmotic stress. Hence, winterkill was likely an important factor eliminating fishes in low salinity lakes that had high productivity and shallow water depth. Ultimately, while salinity was crucial, intricate combinations of chemical and biological mechanisms also played a major role in controlling the assemblages of major taxonomic groups in prairie lakes. PMID:23186395

  8. Deforestation-driven food-web collapse linked to emerging tropical infectious disease, Mycobacterium ulcerans.

    PubMed

    Morris, Aaron L; Guégan, Jean-François; Andreou, Demetra; Marsollier, Laurent; Carolan, Kevin; Le Croller, Marie; Sanhueza, Daniel; Gozlan, Rodolphe E

    2016-12-01

    Generalist microorganisms are the agents of many emerging infectious diseases (EIDs), but their natural life cycles are difficult to predict due to the multiplicity of potential hosts and environmental reservoirs. Among 250 known human EIDs, many have been traced to tropical rain forests and specifically freshwater aquatic systems, which act as an interface between microbe-rich sediments or substrates and terrestrial habitats. Along with the rapid urbanization of developing countries, population encroachment, deforestation, and land-use modifications are expected to increase the risk of EID outbreaks. We show that the freshwater food-web collapse driven by land-use change has a nonlinear effect on the abundance of preferential hosts of a generalist bacterial pathogen, Mycobacterium ulcerans. This leads to an increase of the pathogen within systems at certain levels of environmental disturbance. The complex link between aquatic, terrestrial, and EID processes highlights the potential importance of species community composition and structure and species life history traits in disease risk estimation and mapping. Mechanisms such as the one shown here are also central in predicting how human-induced environmental change, for example, deforestation and changes in land use, may drive emergence.

  9. Seeking Emotional Involvement in Science Education: Food-Chains and Webs.

    ERIC Educational Resources Information Center

    Alsop, Steve

    2001-01-01

    Documents a study of emotion in two grade 8 science classrooms. Describes a lesson on food-chains and webs designed with a conceptual and an emotional agenda. Discusses issues of emotion, sensation and relevance in science teaching. (Author/MM)

  10. Contribution of Allochthonous Carbon Subsidies to the Minho Estuary Lower Food Web

    EPA Science Inventory

    To study the contribution of autochthonous and allochthonous organic matter (OM) sources fuelling the lower food web in Minho River estuary (N-Portugal, Europe), we characterized the carbon (?13C) and nitrogen (?15N) stable isotope ratios of zooplankton and their potential OM sou...

  11. BENTHIC PRODUCTION AS THE BASE FOR FOOD WEBS IN ALASKAN ARCTIC LAKES

    EPA Science Inventory

    Plankton are traditionally viewed as the basis for limnetic food webs, with zooplankton acting as an energy gateway between phytoplanktonic primary producers and fish. Often, benthic production is considered to be important primarily to the benthos and in shallow systems, such as...

  12. Invasive rodents have multiple indirect effects on seabird island invertebrate food web structure.

    PubMed

    Thoresen, Joshua; Towns, David; Leuzinger, Sebastian; Durrett, Mel; Mulder, Christa P H; Wardle, David A

    2017-01-31

    Burrowing seabirds that nest on islands transfer nutrients from the sea, disturb the soil through burrowing, damage tree foliage when landing, and thereby modify the surface litter. However, seabirds are in decline worldwide, as are their community- and ecosystem-level impacts, primarily due to invasive predatory mammals. The direct and indirect effects of seabird decline on communities and ecosystems are inherently complex. Here we employed network analysis, as a means of simplifying ecological complexity, to better understand the effects seabird loss may have on island invertebrate communities. Using data on leaf litter communities, we constructed invertebrate food webs for each of eighteen offshore oceanic islands in north-eastern New Zealand, nine of which have high seabird densities and nine of were invaded by rats. Ten network topological metrics (including entropy, generality and vulnerability) were compared between rat invaded and uninvaded (seabird dominant) islands. We found that on rat-islands the invertebrate food webs were smaller and less complex than on their seabird-dominated counterparts, which may be due to the suppression of seabird derived nutrients and consequent effects on trophic cascades. This decreased complexity of food webs due to the presence of rats is indicative of lower ecosystem resistance via lower trophic redundancy. Our results show that rat effects on island ecosystems are manifested throughout entire food webs, and demonstrate how network analysis may be useful to assess ecosystem recovery status as these invaded islands are restored. This article is protected by copyright. All rights reserved.

  13. SEASONAL DYNAMICS OF PCB ACCUMULATION IN A GREAT LAKES FOOD WEB. (R825151)

    EPA Science Inventory

    Seston, sediment, settling organic matter, and food web members were
    collected from Grand Traverse Bay, Lake Michigan, between April 1997 and
    September 1998 to examine PCB and toxaphene biomagnification. Stable isotopes of
    nitrogen and carbon were analyzed in sampl...

  14. Mercury biomagnification through food webs is affected by physical and chemical characteristics of lakes.

    PubMed

    Clayden, Meredith G; Kidd, Karen A; Wyn, Brianna; Kirk, Jane L; Muir, Derek C G; O'Driscoll, Nelson J

    2013-01-01

    Mercury (Hg) contamination in aquatic systems remains a global concern because the organic form, methyl Hg (MeHg), can biomagnify to harmful concentrations in fish, fish-eating wildlife, and humans. Food web transfer of MeHg has been explored using models of log MeHg versus relative trophic position (nitrogen isotopes, δ(15)N), but regression slopes vary across systems for unknown reasons. In this study, MeHg biomagnification was determined for 11 lake food webs in Kejimkujik National Park, Nova Scotia, Canada, and compared to physical and chemical lake characteristics using principal component and multiple regression analyses. MeHg biomagnification (regression slopes of log MeHg versus baseline-adjusted δ(15)N for fishes and invertebrates) varied significantly across lakes and was higher in systems with lower aqueous nutrient/MeHg/chloride scores. This is one of the largest, consistent data sets available on MeHg biomagnification through temperate lake food webs and the first study to use a principal component and multiple regression approach to understand how lake chemical and physical characteristics interact to affect biomagnification among systems. Overall, our results show that the magnitude of MeHg biomagnification through lake food webs is related to the chemical and physical characteristics of the systems, but the underlying mechanisms warrant further investigation.

  15. Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta

    USGS Publications Warehouse

    Sobczak, W.V.; Cloern, J.E.; Jassby, A.D.; Cole, B.E.; Schraga, T.S.; Arnsberg, A.

    2005-01-01

    Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that detritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production. ?? 2005 Estuarine Research Federation.

  16. HYDROLOGY AND NUTRIENT EFFECTS ON FOOD-WEB STRUCTURE IN TEN LAKE SUPERIOR COASTAL WETLANDS

    EPA Science Inventory

    The manuscript examines the effects of hydrology and nutrient enrichment on food-web structure. We find that the hydraulic residence time is a paramount constraint upon the relative contributions of planktonic versus benthic production to the fish community. Nutrient enrichment...

  17. A new dimension: Evolutionary food web dynamics in two dimensional trait space.

    PubMed

    Ritterskamp, Daniel; Bearup, Daniel; Blasius, Bernd

    2016-09-21

    Species within a habitat are not uniformly distributed. However this aspect of community structure, which is fundamental to many conservation activities, is neglected in the majority of models of food web assembly. To address this issue, we introduce a model which incorporates a second dimension, which can be interpreted as space, into the trait space used in evolutionary food web models. Our results show that the additional trait axis allows the emergence of communities with a much greater range of network structures, similar to the diversity observed in real ecological communities. Moreover, the network properties of the food webs obtained are in good agreement with those of empirical food webs. Community emergence follows a consistent pattern with spread along the second trait axis occurring before the assembly of higher trophic levels. Communities can reach either a static final structure, or constantly evolve. We observe that the relative importance of competition and predation is a key determinant of the network structure and the evolutionary dynamics. The latter are driven by the interaction-competition and predation-between small groups of species. The model remains sufficiently simple that we are able to identify the factors, and mechanisms, which determine the final community state.

  18. Grazing food web view from compound-specific stable isotope analysis of amino acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Knowledge of the trophic position (TP) of organisms in food webs allows ecologists to track energy flow and trophic linkages among organisms in complex networks of ecosystems. Compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a relatively new method with the high p...

  19. Columbia River food webs: Developing a broader scientific foundation for river restoration

    USGS Publications Warehouse

    Alldredge, J. Richard; Beauchamp, David; Bisson, Peter A.; Congleton, James; Henny, Charles; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Naiman, Robert J.; Pearcy, William; Rieman, Bruce; Ruggerone, Greg; Scarnecchia, Dennis; Smouse, Peter; Wood, Chris C.

    2011-01-01

    The objectives of this report are to provide a fundamental understanding of aquatic food webs in the Columbia River Basin and to illustrate and summarize their influences on native fish restoration efforts. The spatial scope addresses tributaries, impoundments, the free-flowing Columbia and Snake rivers, as well as the estuary and plume. Achieving the Council's vision for the Columbia River Fish and Wildlife Program (NPCC 2009-09) of sustaining a "productive and diverse community" that provides "abundant" harvest, is best accomplished through a time-prioritized action plan, one that complements other approaches while addressing important challenges and uncertainties related to the Basin's food webs. Note that the oceanic food webs, although of immense importance in sustaining fish populations, are not considered beyond the plume since they involve an additional set of complex and rapidly evolving issues. An analysis of oceanic food webs of relevance to the Columbia River requires a separately focused effort (e.g., Hoegh- Guldberg and Bruno 2010).

  20. The consistency of a species' response to press perturbations with high food web uncertainty.

    PubMed

    Tunney, Tyler D; Carpenter, Stephen R; Vander Zanden, M Jake

    2017-04-12

    Predicting species responses to perturbations is a fundamental challenge in ecology. Decision makers must often identify management perturbations that are the most likely to deliver a desirable management outcome despite incomplete information on the pattern and strength of food web links. Motivated by a current fishery decline in inland lakes of the Midwestern United States, we evaluate consistency of the responses of a target species (walleye (Sander vitreus)) to press perturbations. We represented food web uncertainty with 196 plausible topological models and applied four perturbations to each one. Frequently the direction of the focal predator response to the same perturbation is not consistent across food web topologies. Simultaneous application of management perturbations led to less consistent outcomes compared to the best single perturbation. However, direct manipulation of the adult focal predator produced a desirable outcome in 78% of 196 plausible topologies. Identifying perturbations that produce consistent outcomes in the face of food web uncertainty can have important implications for natural resource conservation and management efforts. This article is protected by copyright. All rights reserved.

  1. Unpacking brown food-webs: Animal trophic identity reflects rampant microbivory

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Detritivory is the dominant trophic paradigm in most terrestrial, aquatic, and marine ecosystems, yet accurate measurement of consumer trophic position within detrital (= ‘brown’) food-webs has remained impenetrable. Measurement of detritivore trophic position is complicated by the fact that detritu...

  2. Evolutionary food web model based on body masses gives realistic networks with permanent species turnover

    NASA Astrophysics Data System (ADS)

    Allhoff, K. T.; Ritterskamp, D.; Rall, B. C.; Drossel, B.; Guill, C.

    2015-06-01

    The networks of predator-prey interactions in ecological systems are remarkably complex, but nevertheless surprisingly stable in terms of long term persistence of the system as a whole. In order to understand the mechanism driving the complexity and stability of such food webs, we developed an eco-evolutionary model in which new species emerge as modifications of existing ones and dynamic ecological interactions determine which species are viable. The food-web structure thereby emerges from the dynamical interplay between speciation and trophic interactions. The proposed model is less abstract than earlier evolutionary food web models in the sense that all three evolving traits have a clear biological meaning, namely the average body mass of the individuals, the preferred prey body mass, and the width of their potential prey body mass spectrum. We observed networks with a wide range of sizes and structures and high similarity to natural food webs. The model networks exhibit a continuous species turnover, but massive extinction waves that affect more than 50% of the network are not observed.

  3. The Importance of Allochthonous Subsidies to an Estuarine Food Web along a Salinity Gradient

    EPA Science Inventory

    Estuarine food webs function within a heterogeneous mosaic and are supported by a mix of primary producers from both local and distant sources. Processes governing the exchange and consumption of organic matter (OM), however, are poorly understood. To study the contribution of ...

  4. Evolutionary food web model based on body masses gives realistic networks with permanent species turnover

    PubMed Central

    Allhoff, K. T.; Ritterskamp, D.; Rall, B. C.; Drossel, B.; Guill, C.

    2015-01-01

    The networks of predator-prey interactions in ecological systems are remarkably complex, but nevertheless surprisingly stable in terms of long term persistence of the system as a whole. In order to understand the mechanism driving the complexity and stability of such food webs, we developed an eco-evolutionary model in which new species emerge as modifications of existing ones and dynamic ecological interactions determine which species are viable. The food-web structure thereby emerges from the dynamical interplay between speciation and trophic interactions. The proposed model is less abstract than earlier evolutionary food web models in the sense that all three evolving traits have a clear biological meaning, namely the average body mass of the individuals, the preferred prey body mass, and the width of their potential prey body mass spectrum. We observed networks with a wide range of sizes and structures and high similarity to natural food webs. The model networks exhibit a continuous species turnover, but massive extinction waves that affect more than 50% of the network are not observed. PMID:26042870

  5. Non-random food-web assembly at habitat edges increases connectivity and functional redundancy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Habitat fragmentation dramatically alters the spatial configuration of landscapes, with the creation of artificial edges affecting community structure and species interactions. Despite this, it is not known how the different food-webs in adjacent habitats merge at their boundaries, and what the cons...

  6. Effects of light reduction on food webs and associated ecosystem services of Yaquina Bay

    EPA Science Inventory

    Reduced water clarity can affect estuarine primary production but little is known of its subsequent effects to consumer guilds or ecosystem services. We investigated those effects using inverse analysis of modeled food webs of the lower (polyhaline) and upper (mesohaline) reache...

  7. Estuarine consumers utilize marine, estuarine and terrestrial organic matter and provide connectivity among these food webs

    EPA Science Inventory

    The flux of organic matter (OM) across ecosystem boundaries can influence estuarine food web dynamics and productivity. However, this process is seldom investigated taking into account all the adjacent ecosystems (e.g. ocean, river, land) and different hydrological settings (i.e....

  8. The role of a water bug, Sigara striata, in freshwater food webs.

    PubMed

    Klecka, Jan

    2014-01-01

    Freshwater food webs are dominated by aquatic invertebrates whose trophic relationships are often poorly known. Here, I used laboratory experiments to study the role of a water bug, Sigara striata, as a potential predator and prey in food webs of stagnant waters. Multiple-choice predation experiment revealed that Sigara, which had been considered mostly herbivorous, also consumed larvae of Chironomus midges. Because they often occur in high densities and are among the most ubiquitous aquatic insects, Sigara water bugs may be important predators in fresh waters. A second experiment tested the role of Sigara as a potential prey for 13 common invertebrate predators. Mortality of Sigara inflicted by different predators varied widely, especially depending on body mass, foraging mode (ambush/searching) and feeding mode (chewing/suctorial) of the predators. Sigara was highly vulnerable to ambush predators, while searching predators caused on average 8.1 times lower mortality of Sigara. Additionally, suctorial predators consumed on average 6.6 times more Sigara individuals than chewing predators, which supports previous results hinting on potentially different predation pressures of these two types of predators on prey populations. The importance of these two foraging-related traits demonstrates the need to move from body mass based to multiple trait based descriptions of food web structure. Overall, the results suggests that detailed experimental studies of common but insufficiently known species can significantly enhance our understanding of food web structure.

  9. BSAFs and Food Web Modeling for Establishing Contaminant Relationships between Biota and Sediment

    EPA Science Inventory

    The presentation will cover how to measure and evaluate BSAFs (biota-sediment accumulation factors), and how to construct, calibrate, validate, and evaluate food web models. The presentation will also discuss the advantages of the two approaches for establishing contaminant rel...

  10. SHIFTS BETWEEN PERIPHYTON-AND PHYTOPLANKTON-BASED FOOD WEBS IN GREAT LAKES COASTAL WETLANDS

    EPA Science Inventory

    Numerous studies have revealed the importance of algae as an energetic base for wetland food webs. Earlier carbon and nitrogen stable isotope analyses in a Lake Superior coastal wetland (Allouez Bay, WI) indicated that, despite the large amount of vascular plant biobass present, ...

  11. Tracing organophosphorus and brominated flame retardants and plasticizers in an estuarine food web.

    PubMed

    Brandsma, Sicco H; Leonards, Pim E G; Leslie, Heather A; de Boer, Jacob

    2015-02-01

    Nine organophosphorus flame retardants (PFRs) were detected in a pelagic and benthic food web of the Western Scheldt estuary, The Netherlands. Concentrations of several PFRs were an order of magnitude higher than those of the brominated flame retardants (BFRs). However, the detection frequency of the PFRs (6-56%) was lower than that of the BFRs (50-97%). Tris(2-butoxyethyl) phosphate (TBOEP), tris(isobutyl) phosphate (TIBP) and tris(2-chloroisopropyl) phosphate (TCIPP) were the dominant PFRs in sediment with median concentrations of 7.0, 8.1 and 1.8 ng/g dry weight (dw), respectively. PFR levels in the suspended particular matter (SPM) were 2-12 times higher than that in sediment. TBOEP, TCIPP, TIBP, tris(2-chloroethyl) phosphate (TCEP) and tris(phenyl) phosphate (TPHP) were found in organisms higher in the estuarine food web. The highest PFR concentrations in the benthic food web were found in sculpin, goby and lugworm with median concentrations of 17, 7.4, 4.6 and 2.0 ng/g wet weight (ww) for TBOEP, TIBP, TCIPP and TPHP, respectively. Comparable levels were observed in the pelagic food web, BDE209 was the predominant PBDE in sediment and SPM with median concentrations up to 9.7 and 385 ng/g dw, respectively. BDE47 was predominant in the biotic compartment of the food web with highest median levels observed in sculpin and common tern eggs of 79 ng/g lipid weight (lw) (2.5 ng/g ww) and 80 ng/g lw (11 ng/g ww), respectively. Trophic magnification was observed for all PBDEs with the exception of BDE209. Indications of trophic magnification of PFRs were observed in the benthic food web for TBOEP, TCIPP and TCEP with tentative trophic magnification factors of 3.5, 2.2 and 2.6, respectively (p<0.05). Most of the other PFRs showed trophic dilution in both food webs. The relative high PFR levels in several fish species suggest high emissions and substantial exposure of organisms to PFRs in the Western Scheldt.

  12. Spatial and temporal variations in food web structure from newly-opened habitat at hydrothermal vents.

    PubMed

    Gaudron, Sylvie Marylène; Lefebvre, Sébastien; Nunes Jorge, Amandine; Gaill, Françoise; Pradillon, Florence

    2012-06-01

    To highlight the spatio-temporal variability of the food web structure of hydrothermal vent fauna from newly-opened habitat, a series of Titanium Ring for Alvinellid Colonization devices (TRACs) was deployed at TICA site on the East Pacific Rise in 2006. This experiment was conducted for periods of 4 days, 13 days and one month and deployments were aligned along a gradient from the basaltic bottom to the vent openings. δ(13)C values of colonists revealed a narrower range of carbon sources in proximity to vent openings in Alvinella pompejana habitat than in Tevnia jerichonana habitat, separated by a distance of four meters. This was possibly due to a spatial change in available food sources with a possible higher contribution of particulate organic matter (POM) to the siboglinid habitat compared to a higher contribution of microbial primar